| Message ID | 20240814081437.956855-6-samuel.holland@sifive.com (mailing list archive) |
|---|---|
| State | Superseded |
| Headers | show |
| Series | riscv: Userspace pointer masking and tagged address ABI | expand |
| Context | Check | Description |
|---|---|---|
| conchuod/vmtest-fixes-PR | fail | merge-conflict |
On 14/08/2024 10:13, Samuel Holland wrote: > When pointer masking is enabled for userspace, the kernel can accept > tagged pointers as arguments to some system calls. Allow this by > untagging the pointers in access_ok() and the uaccess routines. The > uaccess routines must peform untagging in software because U-mode and > S-mode have entirely separate pointer masking configurations. In fact, > hardware may not even implement pointer masking for S-mode. > > Since the number of tag bits is variable, untagged_addr_remote() needs > to know what PMLEN to use for the remote mm. Therefore, the pointer > masking mode must be the same for all threads sharing an mm. Enforce > this with a lock flag in the mm context, as x86 does for LAM. The flag > gets reset in init_new_context() during fork(), as the new mm is no > longer multithreaded. > > Signed-off-by: Samuel Holland <samuel.holland@sifive.com> > --- > > Changes in v3: > - Use IS_ENABLED instead of #ifdef when possible > - Implement mm_untag_mask() > - Remove pmlen from struct thread_info (now only in mm_context_t) > > Changes in v2: > - Implement untagged_addr_remote() > - Restrict PMLEN changes once a process is multithreaded > > arch/riscv/include/asm/mmu.h | 7 +++ > arch/riscv/include/asm/mmu_context.h | 13 +++++ > arch/riscv/include/asm/uaccess.h | 58 ++++++++++++++++++++-- > arch/riscv/kernel/process.c | 73 ++++++++++++++++++++++++++-- > 4 files changed, 141 insertions(+), 10 deletions(-) > > diff --git a/arch/riscv/include/asm/mmu.h b/arch/riscv/include/asm/mmu.h > index c9e03e9da3dc..1cc90465d75b 100644 > --- a/arch/riscv/include/asm/mmu.h > +++ b/arch/riscv/include/asm/mmu.h > @@ -25,9 +25,16 @@ typedef struct { > #ifdef CONFIG_BINFMT_ELF_FDPIC > unsigned long exec_fdpic_loadmap; > unsigned long interp_fdpic_loadmap; > +#endif > + unsigned long flags; > +#ifdef CONFIG_RISCV_ISA_SUPM > + u8 pmlen; > #endif > } mm_context_t; > > +/* Lock the pointer masking mode because this mm is multithreaded */ > +#define MM_CONTEXT_LOCK_PMLEN 0 > + > #define cntx2asid(cntx) ((cntx) & SATP_ASID_MASK) > #define cntx2version(cntx) ((cntx) & ~SATP_ASID_MASK) > > diff --git a/arch/riscv/include/asm/mmu_context.h b/arch/riscv/include/asm/mmu_context.h > index 7030837adc1a..8c4bc49a3a0f 100644 > --- a/arch/riscv/include/asm/mmu_context.h > +++ b/arch/riscv/include/asm/mmu_context.h > @@ -20,6 +20,9 @@ void switch_mm(struct mm_struct *prev, struct mm_struct *next, > static inline void activate_mm(struct mm_struct *prev, > struct mm_struct *next) > { > +#ifdef CONFIG_RISCV_ISA_SUPM > + next->context.pmlen = 0; > +#endif > switch_mm(prev, next, NULL); > } > > @@ -30,11 +33,21 @@ static inline int init_new_context(struct task_struct *tsk, > #ifdef CONFIG_MMU > atomic_long_set(&mm->context.id, 0); > #endif > + if (IS_ENABLED(CONFIG_RISCV_ISA_SUPM)) > + clear_bit(MM_CONTEXT_LOCK_PMLEN, &mm->context.flags); > return 0; > } > > DECLARE_STATIC_KEY_FALSE(use_asid_allocator); > > +#ifdef CONFIG_RISCV_ISA_SUPM > +#define mm_untag_mask mm_untag_mask > +static inline unsigned long mm_untag_mask(struct mm_struct *mm) > +{ > + return -1UL >> mm->context.pmlen; > +} > +#endif > + > #include <asm-generic/mmu_context.h> > > #endif /* _ASM_RISCV_MMU_CONTEXT_H */ > diff --git a/arch/riscv/include/asm/uaccess.h b/arch/riscv/include/asm/uaccess.h > index 72ec1d9bd3f3..6416559232a2 100644 > --- a/arch/riscv/include/asm/uaccess.h > +++ b/arch/riscv/include/asm/uaccess.h > @@ -9,8 +9,56 @@ > #define _ASM_RISCV_UACCESS_H > > #include <asm/asm-extable.h> > +#include <asm/cpufeature.h> > #include <asm/pgtable.h> /* for TASK_SIZE */ > > +#ifdef CONFIG_RISCV_ISA_SUPM > +static inline unsigned long __untagged_addr(unsigned long addr) > +{ > + if (riscv_has_extension_unlikely(RISCV_ISA_EXT_SUPM)) { > + u8 pmlen = current->mm->context.pmlen; > + > + /* Virtual addresses are sign-extended; physical addresses are zero-extended. */ > + if (IS_ENABLED(CONFIG_MMU)) > + return (long)(addr << pmlen) >> pmlen; > + else > + return (addr << pmlen) >> pmlen; > + } > + > + return addr; > +} > + > +#define untagged_addr(addr) ({ \ > + unsigned long __addr = (__force unsigned long)(addr); \ > + (__force __typeof__(addr))__untagged_addr(__addr); \ > +}) > + > +static inline unsigned long __untagged_addr_remote(struct mm_struct *mm, unsigned long addr) > +{ > + if (riscv_has_extension_unlikely(RISCV_ISA_EXT_SUPM)) { > + u8 pmlen = mm->context.pmlen; > + > + /* Virtual addresses are sign-extended; physical addresses are zero-extended. */ > + if (IS_ENABLED(CONFIG_MMU)) > + return (long)(addr << pmlen) >> pmlen; > + else > + return (addr << pmlen) >> pmlen; > + } > + > + return addr; > +} I should have mentioned that in v2: now that you removed the thread_info pmlen field, __untagged_addr_remote() and __untagged_addr() are almost the same, can you merge them? Thanks! Alex > + > +#define untagged_addr_remote(mm, addr) ({ \ > + unsigned long __addr = (__force unsigned long)(addr); \ > + mmap_assert_locked(mm); \ > + (__force __typeof__(addr))__untagged_addr_remote(mm, __addr); \ > +}) > + > +#define access_ok(addr, size) likely(__access_ok(untagged_addr(addr), size)) > +#else > +#define untagged_addr(addr) (addr) > +#endif > + > /* > * User space memory access functions > */ > @@ -130,7 +178,7 @@ do { \ > */ > #define __get_user(x, ptr) \ > ({ \ > - const __typeof__(*(ptr)) __user *__gu_ptr = (ptr); \ > + const __typeof__(*(ptr)) __user *__gu_ptr = untagged_addr(ptr); \ > long __gu_err = 0; \ > \ > __chk_user_ptr(__gu_ptr); \ > @@ -246,7 +294,7 @@ do { \ > */ > #define __put_user(x, ptr) \ > ({ \ > - __typeof__(*(ptr)) __user *__gu_ptr = (ptr); \ > + __typeof__(*(ptr)) __user *__gu_ptr = untagged_addr(ptr); \ > __typeof__(*__gu_ptr) __val = (x); \ > long __pu_err = 0; \ > \ > @@ -293,13 +341,13 @@ unsigned long __must_check __asm_copy_from_user(void *to, > static inline unsigned long > raw_copy_from_user(void *to, const void __user *from, unsigned long n) > { > - return __asm_copy_from_user(to, from, n); > + return __asm_copy_from_user(to, untagged_addr(from), n); > } > > static inline unsigned long > raw_copy_to_user(void __user *to, const void *from, unsigned long n) > { > - return __asm_copy_to_user(to, from, n); > + return __asm_copy_to_user(untagged_addr(to), from, n); > } > > extern long strncpy_from_user(char *dest, const char __user *src, long count); > @@ -314,7 +362,7 @@ unsigned long __must_check clear_user(void __user *to, unsigned long n) > { > might_fault(); > return access_ok(to, n) ? > - __clear_user(to, n) : n; > + __clear_user(untagged_addr(to), n) : n; > } > > #define __get_kernel_nofault(dst, src, type, err_label) \ > diff --git a/arch/riscv/kernel/process.c b/arch/riscv/kernel/process.c > index 1280a7c4a412..f4d8e5c3bb84 100644 > --- a/arch/riscv/kernel/process.c > +++ b/arch/riscv/kernel/process.c > @@ -203,6 +203,10 @@ int copy_thread(struct task_struct *p, const struct kernel_clone_args *args) > unsigned long tls = args->tls; > struct pt_regs *childregs = task_pt_regs(p); > > + /* Ensure all threads in this mm have the same pointer masking mode. */ > + if (IS_ENABLED(CONFIG_RISCV_ISA_SUPM) && p->mm && (clone_flags & CLONE_VM)) > + set_bit(MM_CONTEXT_LOCK_PMLEN, &p->mm->context.flags); > + > memset(&p->thread.s, 0, sizeof(p->thread.s)); > > /* p->thread holds context to be restored by __switch_to() */ > @@ -248,10 +252,16 @@ enum { > static bool have_user_pmlen_7; > static bool have_user_pmlen_16; > > +/* > + * Control the relaxed ABI allowing tagged user addresses into the kernel. > + */ > +static unsigned int tagged_addr_disabled; > + > long set_tagged_addr_ctrl(struct task_struct *task, unsigned long arg) > { > - unsigned long valid_mask = PR_PMLEN_MASK; > + unsigned long valid_mask = PR_PMLEN_MASK | PR_TAGGED_ADDR_ENABLE; > struct thread_info *ti = task_thread_info(task); > + struct mm_struct *mm = task->mm; > unsigned long pmm; > u8 pmlen; > > @@ -266,16 +276,41 @@ long set_tagged_addr_ctrl(struct task_struct *task, unsigned long arg) > * in case choosing a larger PMLEN has a performance impact. > */ > pmlen = FIELD_GET(PR_PMLEN_MASK, arg); > - if (pmlen == PMLEN_0) > + if (pmlen == PMLEN_0) { > pmm = ENVCFG_PMM_PMLEN_0; > - else if (pmlen <= PMLEN_7 && have_user_pmlen_7) > + } else if (pmlen <= PMLEN_7 && have_user_pmlen_7) { > + pmlen = PMLEN_7; > pmm = ENVCFG_PMM_PMLEN_7; > - else if (pmlen <= PMLEN_16 && have_user_pmlen_16) > + } else if (pmlen <= PMLEN_16 && have_user_pmlen_16) { > + pmlen = PMLEN_16; > pmm = ENVCFG_PMM_PMLEN_16; > - else > + } else { > return -EINVAL; > + } > + > + /* > + * Do not allow the enabling of the tagged address ABI if globally > + * disabled via sysctl abi.tagged_addr_disabled, if pointer masking > + * is disabled for userspace. > + */ > + if (arg & PR_TAGGED_ADDR_ENABLE && (tagged_addr_disabled || !pmlen)) > + return -EINVAL; > + > + if (!(arg & PR_TAGGED_ADDR_ENABLE)) > + pmlen = PMLEN_0; > + > + if (mmap_write_lock_killable(mm)) > + return -EINTR; > + > + if (test_bit(MM_CONTEXT_LOCK_PMLEN, &mm->context.flags) && mm->context.pmlen != pmlen) { > + mmap_write_unlock(mm); > + return -EBUSY; > + } > > envcfg_update_bits(task, ENVCFG_PMM, pmm); > + mm->context.pmlen = pmlen; > + > + mmap_write_unlock(mm); > > return 0; > } > @@ -288,6 +323,10 @@ long get_tagged_addr_ctrl(struct task_struct *task) > if (is_compat_thread(ti)) > return -EINVAL; > > + /* > + * The mm context's pmlen is set only when the tagged address ABI is > + * enabled, so the effective PMLEN must be extracted from envcfg.PMM. > + */ > switch (task->thread.envcfg & ENVCFG_PMM) { > case ENVCFG_PMM_PMLEN_7: > ret = FIELD_PREP(PR_PMLEN_MASK, PMLEN_7); > @@ -297,6 +336,9 @@ long get_tagged_addr_ctrl(struct task_struct *task) > break; > } > > + if (task->mm->context.pmlen) > + ret |= PR_TAGGED_ADDR_ENABLE; > + > return ret; > } > > @@ -306,6 +348,24 @@ static bool try_to_set_pmm(unsigned long value) > return (csr_read_clear(CSR_ENVCFG, ENVCFG_PMM) & ENVCFG_PMM) == value; > } > > +/* > + * Global sysctl to disable the tagged user addresses support. This control > + * only prevents the tagged address ABI enabling via prctl() and does not > + * disable it for tasks that already opted in to the relaxed ABI. > + */ > + > +static struct ctl_table tagged_addr_sysctl_table[] = { > + { > + .procname = "tagged_addr_disabled", > + .mode = 0644, > + .data = &tagged_addr_disabled, > + .maxlen = sizeof(int), > + .proc_handler = proc_dointvec_minmax, > + .extra1 = SYSCTL_ZERO, > + .extra2 = SYSCTL_ONE, > + }, > +}; > + > static int __init tagged_addr_init(void) > { > if (!riscv_has_extension_unlikely(RISCV_ISA_EXT_SUPM)) > @@ -319,6 +379,9 @@ static int __init tagged_addr_init(void) > have_user_pmlen_7 = try_to_set_pmm(ENVCFG_PMM_PMLEN_7); > have_user_pmlen_16 = try_to_set_pmm(ENVCFG_PMM_PMLEN_16); > > + if (!register_sysctl("abi", tagged_addr_sysctl_table)) > + return -EINVAL; > + > return 0; > } > core_initcall(tagged_addr_init);
Hi Alex, On 2024-08-14 10:10 AM, Alexandre Ghiti wrote: > On 14/08/2024 10:13, Samuel Holland wrote: >> When pointer masking is enabled for userspace, the kernel can accept >> tagged pointers as arguments to some system calls. Allow this by >> untagging the pointers in access_ok() and the uaccess routines. The >> uaccess routines must peform untagging in software because U-mode and >> S-mode have entirely separate pointer masking configurations. In fact, >> hardware may not even implement pointer masking for S-mode. >> >> Since the number of tag bits is variable, untagged_addr_remote() needs >> to know what PMLEN to use for the remote mm. Therefore, the pointer >> masking mode must be the same for all threads sharing an mm. Enforce >> this with a lock flag in the mm context, as x86 does for LAM. The flag >> gets reset in init_new_context() during fork(), as the new mm is no >> longer multithreaded. >> >> Signed-off-by: Samuel Holland <samuel.holland@sifive.com> >> --- >> >> Changes in v3: >> - Use IS_ENABLED instead of #ifdef when possible >> - Implement mm_untag_mask() >> - Remove pmlen from struct thread_info (now only in mm_context_t) >> >> Changes in v2: >> - Implement untagged_addr_remote() >> - Restrict PMLEN changes once a process is multithreaded >> >> arch/riscv/include/asm/mmu.h | 7 +++ >> arch/riscv/include/asm/mmu_context.h | 13 +++++ >> arch/riscv/include/asm/uaccess.h | 58 ++++++++++++++++++++-- >> arch/riscv/kernel/process.c | 73 ++++++++++++++++++++++++++-- >> 4 files changed, 141 insertions(+), 10 deletions(-) >> >> diff --git a/arch/riscv/include/asm/mmu.h b/arch/riscv/include/asm/mmu.h >> index c9e03e9da3dc..1cc90465d75b 100644 >> --- a/arch/riscv/include/asm/mmu.h >> +++ b/arch/riscv/include/asm/mmu.h >> @@ -25,9 +25,16 @@ typedef struct { >> #ifdef CONFIG_BINFMT_ELF_FDPIC >> unsigned long exec_fdpic_loadmap; >> unsigned long interp_fdpic_loadmap; >> +#endif >> + unsigned long flags; >> +#ifdef CONFIG_RISCV_ISA_SUPM >> + u8 pmlen; >> #endif >> } mm_context_t; >> +/* Lock the pointer masking mode because this mm is multithreaded */ >> +#define MM_CONTEXT_LOCK_PMLEN 0 >> + >> #define cntx2asid(cntx) ((cntx) & SATP_ASID_MASK) >> #define cntx2version(cntx) ((cntx) & ~SATP_ASID_MASK) >> diff --git a/arch/riscv/include/asm/mmu_context.h >> b/arch/riscv/include/asm/mmu_context.h >> index 7030837adc1a..8c4bc49a3a0f 100644 >> --- a/arch/riscv/include/asm/mmu_context.h >> +++ b/arch/riscv/include/asm/mmu_context.h >> @@ -20,6 +20,9 @@ void switch_mm(struct mm_struct *prev, struct mm_struct *next, >> static inline void activate_mm(struct mm_struct *prev, >> struct mm_struct *next) >> { >> +#ifdef CONFIG_RISCV_ISA_SUPM >> + next->context.pmlen = 0; >> +#endif >> switch_mm(prev, next, NULL); >> } >> @@ -30,11 +33,21 @@ static inline int init_new_context(struct task_struct *tsk, >> #ifdef CONFIG_MMU >> atomic_long_set(&mm->context.id, 0); >> #endif >> + if (IS_ENABLED(CONFIG_RISCV_ISA_SUPM)) >> + clear_bit(MM_CONTEXT_LOCK_PMLEN, &mm->context.flags); >> return 0; >> } >> DECLARE_STATIC_KEY_FALSE(use_asid_allocator); >> +#ifdef CONFIG_RISCV_ISA_SUPM >> +#define mm_untag_mask mm_untag_mask >> +static inline unsigned long mm_untag_mask(struct mm_struct *mm) >> +{ >> + return -1UL >> mm->context.pmlen; >> +} >> +#endif >> + >> #include <asm-generic/mmu_context.h> >> #endif /* _ASM_RISCV_MMU_CONTEXT_H */ >> diff --git a/arch/riscv/include/asm/uaccess.h b/arch/riscv/include/asm/uaccess.h >> index 72ec1d9bd3f3..6416559232a2 100644 >> --- a/arch/riscv/include/asm/uaccess.h >> +++ b/arch/riscv/include/asm/uaccess.h >> @@ -9,8 +9,56 @@ >> #define _ASM_RISCV_UACCESS_H >> #include <asm/asm-extable.h> >> +#include <asm/cpufeature.h> >> #include <asm/pgtable.h> /* for TASK_SIZE */ >> +#ifdef CONFIG_RISCV_ISA_SUPM >> +static inline unsigned long __untagged_addr(unsigned long addr) >> +{ >> + if (riscv_has_extension_unlikely(RISCV_ISA_EXT_SUPM)) { >> + u8 pmlen = current->mm->context.pmlen; >> + >> + /* Virtual addresses are sign-extended; physical addresses are >> zero-extended. */ >> + if (IS_ENABLED(CONFIG_MMU)) >> + return (long)(addr << pmlen) >> pmlen; >> + else >> + return (addr << pmlen) >> pmlen; >> + } >> + >> + return addr; >> +} >> + >> +#define untagged_addr(addr) ({ \ >> + unsigned long __addr = (__force unsigned long)(addr); \ >> + (__force __typeof__(addr))__untagged_addr(__addr); \ >> +}) >> + >> +static inline unsigned long __untagged_addr_remote(struct mm_struct *mm, >> unsigned long addr) >> +{ >> + if (riscv_has_extension_unlikely(RISCV_ISA_EXT_SUPM)) { >> + u8 pmlen = mm->context.pmlen; >> + >> + /* Virtual addresses are sign-extended; physical addresses are >> zero-extended. */ >> + if (IS_ENABLED(CONFIG_MMU)) >> + return (long)(addr << pmlen) >> pmlen; >> + else >> + return (addr << pmlen) >> pmlen; >> + } >> + >> + return addr; >> +} > > > I should have mentioned that in v2: now that you removed the thread_info pmlen > field, __untagged_addr_remote() and __untagged_addr() are almost the same, can > you merge them? I can merge them, but this places the load of current->mm outside the static branch. If you think that is okay, then I'll merge them for v4. Regards, Samuel >> + >> +#define untagged_addr_remote(mm, addr) ({ \ >> + unsigned long __addr = (__force unsigned long)(addr); \ >> + mmap_assert_locked(mm); \ >> + (__force __typeof__(addr))__untagged_addr_remote(mm, __addr); \ >> +}) >> + >> +#define access_ok(addr, size) likely(__access_ok(untagged_addr(addr), size)) >> +#else >> +#define untagged_addr(addr) (addr) >> +#endif >> + >> /* >> * User space memory access functions >> */ >> @@ -130,7 +178,7 @@ do { \ >> */ >> #define __get_user(x, ptr) \ >> ({ \ >> - const __typeof__(*(ptr)) __user *__gu_ptr = (ptr); \ >> + const __typeof__(*(ptr)) __user *__gu_ptr = untagged_addr(ptr); \ >> long __gu_err = 0; \ >> \ >> __chk_user_ptr(__gu_ptr); \ >> @@ -246,7 +294,7 @@ do { \ >> */ >> #define __put_user(x, ptr) \ >> ({ \ >> - __typeof__(*(ptr)) __user *__gu_ptr = (ptr); \ >> + __typeof__(*(ptr)) __user *__gu_ptr = untagged_addr(ptr); \ >> __typeof__(*__gu_ptr) __val = (x); \ >> long __pu_err = 0; \ >> \ >> @@ -293,13 +341,13 @@ unsigned long __must_check __asm_copy_from_user(void *to, >> static inline unsigned long >> raw_copy_from_user(void *to, const void __user *from, unsigned long n) >> { >> - return __asm_copy_from_user(to, from, n); >> + return __asm_copy_from_user(to, untagged_addr(from), n); >> } >> static inline unsigned long >> raw_copy_to_user(void __user *to, const void *from, unsigned long n) >> { >> - return __asm_copy_to_user(to, from, n); >> + return __asm_copy_to_user(untagged_addr(to), from, n); >> } >> extern long strncpy_from_user(char *dest, const char __user *src, long >> count); >> @@ -314,7 +362,7 @@ unsigned long __must_check clear_user(void __user *to, >> unsigned long n) >> { >> might_fault(); >> return access_ok(to, n) ? >> - __clear_user(to, n) : n; >> + __clear_user(untagged_addr(to), n) : n; >> } >> #define __get_kernel_nofault(dst, src, type, err_label) \ >> diff --git a/arch/riscv/kernel/process.c b/arch/riscv/kernel/process.c >> index 1280a7c4a412..f4d8e5c3bb84 100644 >> --- a/arch/riscv/kernel/process.c >> +++ b/arch/riscv/kernel/process.c >> @@ -203,6 +203,10 @@ int copy_thread(struct task_struct *p, const struct >> kernel_clone_args *args) >> unsigned long tls = args->tls; >> struct pt_regs *childregs = task_pt_regs(p); >> + /* Ensure all threads in this mm have the same pointer masking mode. */ >> + if (IS_ENABLED(CONFIG_RISCV_ISA_SUPM) && p->mm && (clone_flags & CLONE_VM)) >> + set_bit(MM_CONTEXT_LOCK_PMLEN, &p->mm->context.flags); >> + >> memset(&p->thread.s, 0, sizeof(p->thread.s)); >> /* p->thread holds context to be restored by __switch_to() */ >> @@ -248,10 +252,16 @@ enum { >> static bool have_user_pmlen_7; >> static bool have_user_pmlen_16; >> +/* >> + * Control the relaxed ABI allowing tagged user addresses into the kernel. >> + */ >> +static unsigned int tagged_addr_disabled; >> + >> long set_tagged_addr_ctrl(struct task_struct *task, unsigned long arg) >> { >> - unsigned long valid_mask = PR_PMLEN_MASK; >> + unsigned long valid_mask = PR_PMLEN_MASK | PR_TAGGED_ADDR_ENABLE; >> struct thread_info *ti = task_thread_info(task); >> + struct mm_struct *mm = task->mm; >> unsigned long pmm; >> u8 pmlen; >> @@ -266,16 +276,41 @@ long set_tagged_addr_ctrl(struct task_struct *task, >> unsigned long arg) >> * in case choosing a larger PMLEN has a performance impact. >> */ >> pmlen = FIELD_GET(PR_PMLEN_MASK, arg); >> - if (pmlen == PMLEN_0) >> + if (pmlen == PMLEN_0) { >> pmm = ENVCFG_PMM_PMLEN_0; >> - else if (pmlen <= PMLEN_7 && have_user_pmlen_7) >> + } else if (pmlen <= PMLEN_7 && have_user_pmlen_7) { >> + pmlen = PMLEN_7; >> pmm = ENVCFG_PMM_PMLEN_7; >> - else if (pmlen <= PMLEN_16 && have_user_pmlen_16) >> + } else if (pmlen <= PMLEN_16 && have_user_pmlen_16) { >> + pmlen = PMLEN_16; >> pmm = ENVCFG_PMM_PMLEN_16; >> - else >> + } else { >> return -EINVAL; >> + } >> + >> + /* >> + * Do not allow the enabling of the tagged address ABI if globally >> + * disabled via sysctl abi.tagged_addr_disabled, if pointer masking >> + * is disabled for userspace. >> + */ >> + if (arg & PR_TAGGED_ADDR_ENABLE && (tagged_addr_disabled || !pmlen)) >> + return -EINVAL; >> + >> + if (!(arg & PR_TAGGED_ADDR_ENABLE)) >> + pmlen = PMLEN_0; >> + >> + if (mmap_write_lock_killable(mm)) >> + return -EINTR; >> + >> + if (test_bit(MM_CONTEXT_LOCK_PMLEN, &mm->context.flags) && >> mm->context.pmlen != pmlen) { >> + mmap_write_unlock(mm); >> + return -EBUSY; >> + } >> envcfg_update_bits(task, ENVCFG_PMM, pmm); >> + mm->context.pmlen = pmlen; >> + >> + mmap_write_unlock(mm); >> return 0; >> } >> @@ -288,6 +323,10 @@ long get_tagged_addr_ctrl(struct task_struct *task) >> if (is_compat_thread(ti)) >> return -EINVAL; >> + /* >> + * The mm context's pmlen is set only when the tagged address ABI is >> + * enabled, so the effective PMLEN must be extracted from envcfg.PMM. >> + */ >> switch (task->thread.envcfg & ENVCFG_PMM) { >> case ENVCFG_PMM_PMLEN_7: >> ret = FIELD_PREP(PR_PMLEN_MASK, PMLEN_7); >> @@ -297,6 +336,9 @@ long get_tagged_addr_ctrl(struct task_struct *task) >> break; >> } >> + if (task->mm->context.pmlen) >> + ret |= PR_TAGGED_ADDR_ENABLE; >> + >> return ret; >> } >> @@ -306,6 +348,24 @@ static bool try_to_set_pmm(unsigned long value) >> return (csr_read_clear(CSR_ENVCFG, ENVCFG_PMM) & ENVCFG_PMM) == value; >> } >> +/* >> + * Global sysctl to disable the tagged user addresses support. This control >> + * only prevents the tagged address ABI enabling via prctl() and does not >> + * disable it for tasks that already opted in to the relaxed ABI. >> + */ >> + >> +static struct ctl_table tagged_addr_sysctl_table[] = { >> + { >> + .procname = "tagged_addr_disabled", >> + .mode = 0644, >> + .data = &tagged_addr_disabled, >> + .maxlen = sizeof(int), >> + .proc_handler = proc_dointvec_minmax, >> + .extra1 = SYSCTL_ZERO, >> + .extra2 = SYSCTL_ONE, >> + }, >> +}; >> + >> static int __init tagged_addr_init(void) >> { >> if (!riscv_has_extension_unlikely(RISCV_ISA_EXT_SUPM)) >> @@ -319,6 +379,9 @@ static int __init tagged_addr_init(void) >> have_user_pmlen_7 = try_to_set_pmm(ENVCFG_PMM_PMLEN_7); >> have_user_pmlen_16 = try_to_set_pmm(ENVCFG_PMM_PMLEN_16); >> + if (!register_sysctl("abi", tagged_addr_sysctl_table)) >> + return -EINVAL; >> + >> return 0; >> } >> core_initcall(tagged_addr_init);
On 14/08/2024 18:14, Samuel Holland wrote: > Hi Alex, > > On 2024-08-14 10:10 AM, Alexandre Ghiti wrote: >> On 14/08/2024 10:13, Samuel Holland wrote: >>> When pointer masking is enabled for userspace, the kernel can accept >>> tagged pointers as arguments to some system calls. Allow this by >>> untagging the pointers in access_ok() and the uaccess routines. The >>> uaccess routines must peform untagging in software because U-mode and >>> S-mode have entirely separate pointer masking configurations. In fact, >>> hardware may not even implement pointer masking for S-mode. >>> >>> Since the number of tag bits is variable, untagged_addr_remote() needs >>> to know what PMLEN to use for the remote mm. Therefore, the pointer >>> masking mode must be the same for all threads sharing an mm. Enforce >>> this with a lock flag in the mm context, as x86 does for LAM. The flag >>> gets reset in init_new_context() during fork(), as the new mm is no >>> longer multithreaded. >>> >>> Signed-off-by: Samuel Holland <samuel.holland@sifive.com> >>> --- >>> >>> Changes in v3: >>> - Use IS_ENABLED instead of #ifdef when possible >>> - Implement mm_untag_mask() >>> - Remove pmlen from struct thread_info (now only in mm_context_t) >>> >>> Changes in v2: >>> - Implement untagged_addr_remote() >>> - Restrict PMLEN changes once a process is multithreaded >>> >>> arch/riscv/include/asm/mmu.h | 7 +++ >>> arch/riscv/include/asm/mmu_context.h | 13 +++++ >>> arch/riscv/include/asm/uaccess.h | 58 ++++++++++++++++++++-- >>> arch/riscv/kernel/process.c | 73 ++++++++++++++++++++++++++-- >>> 4 files changed, 141 insertions(+), 10 deletions(-) >>> >>> diff --git a/arch/riscv/include/asm/mmu.h b/arch/riscv/include/asm/mmu.h >>> index c9e03e9da3dc..1cc90465d75b 100644 >>> --- a/arch/riscv/include/asm/mmu.h >>> +++ b/arch/riscv/include/asm/mmu.h >>> @@ -25,9 +25,16 @@ typedef struct { >>> #ifdef CONFIG_BINFMT_ELF_FDPIC >>> unsigned long exec_fdpic_loadmap; >>> unsigned long interp_fdpic_loadmap; >>> +#endif >>> + unsigned long flags; >>> +#ifdef CONFIG_RISCV_ISA_SUPM >>> + u8 pmlen; >>> #endif >>> } mm_context_t; >>> +/* Lock the pointer masking mode because this mm is multithreaded */ >>> +#define MM_CONTEXT_LOCK_PMLEN 0 >>> + >>> #define cntx2asid(cntx) ((cntx) & SATP_ASID_MASK) >>> #define cntx2version(cntx) ((cntx) & ~SATP_ASID_MASK) >>> diff --git a/arch/riscv/include/asm/mmu_context.h >>> b/arch/riscv/include/asm/mmu_context.h >>> index 7030837adc1a..8c4bc49a3a0f 100644 >>> --- a/arch/riscv/include/asm/mmu_context.h >>> +++ b/arch/riscv/include/asm/mmu_context.h >>> @@ -20,6 +20,9 @@ void switch_mm(struct mm_struct *prev, struct mm_struct *next, >>> static inline void activate_mm(struct mm_struct *prev, >>> struct mm_struct *next) >>> { >>> +#ifdef CONFIG_RISCV_ISA_SUPM >>> + next->context.pmlen = 0; >>> +#endif >>> switch_mm(prev, next, NULL); >>> } >>> @@ -30,11 +33,21 @@ static inline int init_new_context(struct task_struct *tsk, >>> #ifdef CONFIG_MMU >>> atomic_long_set(&mm->context.id, 0); >>> #endif >>> + if (IS_ENABLED(CONFIG_RISCV_ISA_SUPM)) >>> + clear_bit(MM_CONTEXT_LOCK_PMLEN, &mm->context.flags); >>> return 0; >>> } >>> DECLARE_STATIC_KEY_FALSE(use_asid_allocator); >>> +#ifdef CONFIG_RISCV_ISA_SUPM >>> +#define mm_untag_mask mm_untag_mask >>> +static inline unsigned long mm_untag_mask(struct mm_struct *mm) >>> +{ >>> + return -1UL >> mm->context.pmlen; >>> +} >>> +#endif >>> + >>> #include <asm-generic/mmu_context.h> >>> #endif /* _ASM_RISCV_MMU_CONTEXT_H */ >>> diff --git a/arch/riscv/include/asm/uaccess.h b/arch/riscv/include/asm/uaccess.h >>> index 72ec1d9bd3f3..6416559232a2 100644 >>> --- a/arch/riscv/include/asm/uaccess.h >>> +++ b/arch/riscv/include/asm/uaccess.h >>> @@ -9,8 +9,56 @@ >>> #define _ASM_RISCV_UACCESS_H >>> #include <asm/asm-extable.h> >>> +#include <asm/cpufeature.h> >>> #include <asm/pgtable.h> /* for TASK_SIZE */ >>> +#ifdef CONFIG_RISCV_ISA_SUPM >>> +static inline unsigned long __untagged_addr(unsigned long addr) >>> +{ >>> + if (riscv_has_extension_unlikely(RISCV_ISA_EXT_SUPM)) { >>> + u8 pmlen = current->mm->context.pmlen; >>> + >>> + /* Virtual addresses are sign-extended; physical addresses are >>> zero-extended. */ >>> + if (IS_ENABLED(CONFIG_MMU)) >>> + return (long)(addr << pmlen) >> pmlen; >>> + else >>> + return (addr << pmlen) >> pmlen; >>> + } >>> + >>> + return addr; >>> +} >>> + >>> +#define untagged_addr(addr) ({ \ >>> + unsigned long __addr = (__force unsigned long)(addr); \ >>> + (__force __typeof__(addr))__untagged_addr(__addr); \ >>> +}) >>> + >>> +static inline unsigned long __untagged_addr_remote(struct mm_struct *mm, >>> unsigned long addr) >>> +{ >>> + if (riscv_has_extension_unlikely(RISCV_ISA_EXT_SUPM)) { >>> + u8 pmlen = mm->context.pmlen; >>> + >>> + /* Virtual addresses are sign-extended; physical addresses are >>> zero-extended. */ >>> + if (IS_ENABLED(CONFIG_MMU)) >>> + return (long)(addr << pmlen) >> pmlen; >>> + else >>> + return (addr << pmlen) >> pmlen; >>> + } >>> + >>> + return addr; >>> +} >> >> I should have mentioned that in v2: now that you removed the thread_info pmlen >> field, __untagged_addr_remote() and __untagged_addr() are almost the same, can >> you merge them? > I can merge them, but this places the load of current->mm outside the static > branch. If you think that is okay, then I'll merge them for v4. I think it's ok, it's not a big overhead :) Thanks, Alex > Regards, > Samuel > >>> + >>> +#define untagged_addr_remote(mm, addr) ({ \ >>> + unsigned long __addr = (__force unsigned long)(addr); \ >>> + mmap_assert_locked(mm); \ >>> + (__force __typeof__(addr))__untagged_addr_remote(mm, __addr); \ >>> +}) >>> + >>> +#define access_ok(addr, size) likely(__access_ok(untagged_addr(addr), size)) >>> +#else >>> +#define untagged_addr(addr) (addr) >>> +#endif >>> + >>> /* >>> * User space memory access functions >>> */ >>> @@ -130,7 +178,7 @@ do { \ >>> */ >>> #define __get_user(x, ptr) \ >>> ({ \ >>> - const __typeof__(*(ptr)) __user *__gu_ptr = (ptr); \ >>> + const __typeof__(*(ptr)) __user *__gu_ptr = untagged_addr(ptr); \ >>> long __gu_err = 0; \ >>> \ >>> __chk_user_ptr(__gu_ptr); \ >>> @@ -246,7 +294,7 @@ do { \ >>> */ >>> #define __put_user(x, ptr) \ >>> ({ \ >>> - __typeof__(*(ptr)) __user *__gu_ptr = (ptr); \ >>> + __typeof__(*(ptr)) __user *__gu_ptr = untagged_addr(ptr); \ >>> __typeof__(*__gu_ptr) __val = (x); \ >>> long __pu_err = 0; \ >>> \ >>> @@ -293,13 +341,13 @@ unsigned long __must_check __asm_copy_from_user(void *to, >>> static inline unsigned long >>> raw_copy_from_user(void *to, const void __user *from, unsigned long n) >>> { >>> - return __asm_copy_from_user(to, from, n); >>> + return __asm_copy_from_user(to, untagged_addr(from), n); >>> } >>> static inline unsigned long >>> raw_copy_to_user(void __user *to, const void *from, unsigned long n) >>> { >>> - return __asm_copy_to_user(to, from, n); >>> + return __asm_copy_to_user(untagged_addr(to), from, n); >>> } >>> extern long strncpy_from_user(char *dest, const char __user *src, long >>> count); >>> @@ -314,7 +362,7 @@ unsigned long __must_check clear_user(void __user *to, >>> unsigned long n) >>> { >>> might_fault(); >>> return access_ok(to, n) ? >>> - __clear_user(to, n) : n; >>> + __clear_user(untagged_addr(to), n) : n; >>> } >>> #define __get_kernel_nofault(dst, src, type, err_label) \ >>> diff --git a/arch/riscv/kernel/process.c b/arch/riscv/kernel/process.c >>> index 1280a7c4a412..f4d8e5c3bb84 100644 >>> --- a/arch/riscv/kernel/process.c >>> +++ b/arch/riscv/kernel/process.c >>> @@ -203,6 +203,10 @@ int copy_thread(struct task_struct *p, const struct >>> kernel_clone_args *args) >>> unsigned long tls = args->tls; >>> struct pt_regs *childregs = task_pt_regs(p); >>> + /* Ensure all threads in this mm have the same pointer masking mode. */ >>> + if (IS_ENABLED(CONFIG_RISCV_ISA_SUPM) && p->mm && (clone_flags & CLONE_VM)) >>> + set_bit(MM_CONTEXT_LOCK_PMLEN, &p->mm->context.flags); >>> + >>> memset(&p->thread.s, 0, sizeof(p->thread.s)); >>> /* p->thread holds context to be restored by __switch_to() */ >>> @@ -248,10 +252,16 @@ enum { >>> static bool have_user_pmlen_7; >>> static bool have_user_pmlen_16; >>> +/* >>> + * Control the relaxed ABI allowing tagged user addresses into the kernel. >>> + */ >>> +static unsigned int tagged_addr_disabled; >>> + >>> long set_tagged_addr_ctrl(struct task_struct *task, unsigned long arg) >>> { >>> - unsigned long valid_mask = PR_PMLEN_MASK; >>> + unsigned long valid_mask = PR_PMLEN_MASK | PR_TAGGED_ADDR_ENABLE; >>> struct thread_info *ti = task_thread_info(task); >>> + struct mm_struct *mm = task->mm; >>> unsigned long pmm; >>> u8 pmlen; >>> @@ -266,16 +276,41 @@ long set_tagged_addr_ctrl(struct task_struct *task, >>> unsigned long arg) >>> * in case choosing a larger PMLEN has a performance impact. >>> */ >>> pmlen = FIELD_GET(PR_PMLEN_MASK, arg); >>> - if (pmlen == PMLEN_0) >>> + if (pmlen == PMLEN_0) { >>> pmm = ENVCFG_PMM_PMLEN_0; >>> - else if (pmlen <= PMLEN_7 && have_user_pmlen_7) >>> + } else if (pmlen <= PMLEN_7 && have_user_pmlen_7) { >>> + pmlen = PMLEN_7; >>> pmm = ENVCFG_PMM_PMLEN_7; >>> - else if (pmlen <= PMLEN_16 && have_user_pmlen_16) >>> + } else if (pmlen <= PMLEN_16 && have_user_pmlen_16) { >>> + pmlen = PMLEN_16; >>> pmm = ENVCFG_PMM_PMLEN_16; >>> - else >>> + } else { >>> return -EINVAL; >>> + } >>> + >>> + /* >>> + * Do not allow the enabling of the tagged address ABI if globally >>> + * disabled via sysctl abi.tagged_addr_disabled, if pointer masking >>> + * is disabled for userspace. >>> + */ >>> + if (arg & PR_TAGGED_ADDR_ENABLE && (tagged_addr_disabled || !pmlen)) >>> + return -EINVAL; >>> + >>> + if (!(arg & PR_TAGGED_ADDR_ENABLE)) >>> + pmlen = PMLEN_0; >>> + >>> + if (mmap_write_lock_killable(mm)) >>> + return -EINTR; >>> + >>> + if (test_bit(MM_CONTEXT_LOCK_PMLEN, &mm->context.flags) && >>> mm->context.pmlen != pmlen) { >>> + mmap_write_unlock(mm); >>> + return -EBUSY; >>> + } >>> envcfg_update_bits(task, ENVCFG_PMM, pmm); >>> + mm->context.pmlen = pmlen; >>> + >>> + mmap_write_unlock(mm); >>> return 0; >>> } >>> @@ -288,6 +323,10 @@ long get_tagged_addr_ctrl(struct task_struct *task) >>> if (is_compat_thread(ti)) >>> return -EINVAL; >>> + /* >>> + * The mm context's pmlen is set only when the tagged address ABI is >>> + * enabled, so the effective PMLEN must be extracted from envcfg.PMM. >>> + */ >>> switch (task->thread.envcfg & ENVCFG_PMM) { >>> case ENVCFG_PMM_PMLEN_7: >>> ret = FIELD_PREP(PR_PMLEN_MASK, PMLEN_7); >>> @@ -297,6 +336,9 @@ long get_tagged_addr_ctrl(struct task_struct *task) >>> break; >>> } >>> + if (task->mm->context.pmlen) >>> + ret |= PR_TAGGED_ADDR_ENABLE; >>> + >>> return ret; >>> } >>> @@ -306,6 +348,24 @@ static bool try_to_set_pmm(unsigned long value) >>> return (csr_read_clear(CSR_ENVCFG, ENVCFG_PMM) & ENVCFG_PMM) == value; >>> } >>> +/* >>> + * Global sysctl to disable the tagged user addresses support. This control >>> + * only prevents the tagged address ABI enabling via prctl() and does not >>> + * disable it for tasks that already opted in to the relaxed ABI. >>> + */ >>> + >>> +static struct ctl_table tagged_addr_sysctl_table[] = { >>> + { >>> + .procname = "tagged_addr_disabled", >>> + .mode = 0644, >>> + .data = &tagged_addr_disabled, >>> + .maxlen = sizeof(int), >>> + .proc_handler = proc_dointvec_minmax, >>> + .extra1 = SYSCTL_ZERO, >>> + .extra2 = SYSCTL_ONE, >>> + }, >>> +}; >>> + >>> static int __init tagged_addr_init(void) >>> { >>> if (!riscv_has_extension_unlikely(RISCV_ISA_EXT_SUPM)) >>> @@ -319,6 +379,9 @@ static int __init tagged_addr_init(void) >>> have_user_pmlen_7 = try_to_set_pmm(ENVCFG_PMM_PMLEN_7); >>> have_user_pmlen_16 = try_to_set_pmm(ENVCFG_PMM_PMLEN_16); >>> + if (!register_sysctl("abi", tagged_addr_sysctl_table)) >>> + return -EINVAL; >>> + >>> return 0; >>> } >>> core_initcall(tagged_addr_init); > > _______________________________________________ > linux-riscv mailing list > linux-riscv@lists.infradead.org > http://lists.infradead.org/mailman/listinfo/linux-riscv
diff --git a/arch/riscv/include/asm/mmu.h b/arch/riscv/include/asm/mmu.h index c9e03e9da3dc..1cc90465d75b 100644 --- a/arch/riscv/include/asm/mmu.h +++ b/arch/riscv/include/asm/mmu.h @@ -25,9 +25,16 @@ typedef struct { #ifdef CONFIG_BINFMT_ELF_FDPIC unsigned long exec_fdpic_loadmap; unsigned long interp_fdpic_loadmap; +#endif + unsigned long flags; +#ifdef CONFIG_RISCV_ISA_SUPM + u8 pmlen; #endif } mm_context_t; +/* Lock the pointer masking mode because this mm is multithreaded */ +#define MM_CONTEXT_LOCK_PMLEN 0 + #define cntx2asid(cntx) ((cntx) & SATP_ASID_MASK) #define cntx2version(cntx) ((cntx) & ~SATP_ASID_MASK) diff --git a/arch/riscv/include/asm/mmu_context.h b/arch/riscv/include/asm/mmu_context.h index 7030837adc1a..8c4bc49a3a0f 100644 --- a/arch/riscv/include/asm/mmu_context.h +++ b/arch/riscv/include/asm/mmu_context.h @@ -20,6 +20,9 @@ void switch_mm(struct mm_struct *prev, struct mm_struct *next, static inline void activate_mm(struct mm_struct *prev, struct mm_struct *next) { +#ifdef CONFIG_RISCV_ISA_SUPM + next->context.pmlen = 0; +#endif switch_mm(prev, next, NULL); } @@ -30,11 +33,21 @@ static inline int init_new_context(struct task_struct *tsk, #ifdef CONFIG_MMU atomic_long_set(&mm->context.id, 0); #endif + if (IS_ENABLED(CONFIG_RISCV_ISA_SUPM)) + clear_bit(MM_CONTEXT_LOCK_PMLEN, &mm->context.flags); return 0; } DECLARE_STATIC_KEY_FALSE(use_asid_allocator); +#ifdef CONFIG_RISCV_ISA_SUPM +#define mm_untag_mask mm_untag_mask +static inline unsigned long mm_untag_mask(struct mm_struct *mm) +{ + return -1UL >> mm->context.pmlen; +} +#endif + #include <asm-generic/mmu_context.h> #endif /* _ASM_RISCV_MMU_CONTEXT_H */ diff --git a/arch/riscv/include/asm/uaccess.h b/arch/riscv/include/asm/uaccess.h index 72ec1d9bd3f3..6416559232a2 100644 --- a/arch/riscv/include/asm/uaccess.h +++ b/arch/riscv/include/asm/uaccess.h @@ -9,8 +9,56 @@ #define _ASM_RISCV_UACCESS_H #include <asm/asm-extable.h> +#include <asm/cpufeature.h> #include <asm/pgtable.h> /* for TASK_SIZE */ +#ifdef CONFIG_RISCV_ISA_SUPM +static inline unsigned long __untagged_addr(unsigned long addr) +{ + if (riscv_has_extension_unlikely(RISCV_ISA_EXT_SUPM)) { + u8 pmlen = current->mm->context.pmlen; + + /* Virtual addresses are sign-extended; physical addresses are zero-extended. */ + if (IS_ENABLED(CONFIG_MMU)) + return (long)(addr << pmlen) >> pmlen; + else + return (addr << pmlen) >> pmlen; + } + + return addr; +} + +#define untagged_addr(addr) ({ \ + unsigned long __addr = (__force unsigned long)(addr); \ + (__force __typeof__(addr))__untagged_addr(__addr); \ +}) + +static inline unsigned long __untagged_addr_remote(struct mm_struct *mm, unsigned long addr) +{ + if (riscv_has_extension_unlikely(RISCV_ISA_EXT_SUPM)) { + u8 pmlen = mm->context.pmlen; + + /* Virtual addresses are sign-extended; physical addresses are zero-extended. */ + if (IS_ENABLED(CONFIG_MMU)) + return (long)(addr << pmlen) >> pmlen; + else + return (addr << pmlen) >> pmlen; + } + + return addr; +} + +#define untagged_addr_remote(mm, addr) ({ \ + unsigned long __addr = (__force unsigned long)(addr); \ + mmap_assert_locked(mm); \ + (__force __typeof__(addr))__untagged_addr_remote(mm, __addr); \ +}) + +#define access_ok(addr, size) likely(__access_ok(untagged_addr(addr), size)) +#else +#define untagged_addr(addr) (addr) +#endif + /* * User space memory access functions */ @@ -130,7 +178,7 @@ do { \ */ #define __get_user(x, ptr) \ ({ \ - const __typeof__(*(ptr)) __user *__gu_ptr = (ptr); \ + const __typeof__(*(ptr)) __user *__gu_ptr = untagged_addr(ptr); \ long __gu_err = 0; \ \ __chk_user_ptr(__gu_ptr); \ @@ -246,7 +294,7 @@ do { \ */ #define __put_user(x, ptr) \ ({ \ - __typeof__(*(ptr)) __user *__gu_ptr = (ptr); \ + __typeof__(*(ptr)) __user *__gu_ptr = untagged_addr(ptr); \ __typeof__(*__gu_ptr) __val = (x); \ long __pu_err = 0; \ \ @@ -293,13 +341,13 @@ unsigned long __must_check __asm_copy_from_user(void *to, static inline unsigned long raw_copy_from_user(void *to, const void __user *from, unsigned long n) { - return __asm_copy_from_user(to, from, n); + return __asm_copy_from_user(to, untagged_addr(from), n); } static inline unsigned long raw_copy_to_user(void __user *to, const void *from, unsigned long n) { - return __asm_copy_to_user(to, from, n); + return __asm_copy_to_user(untagged_addr(to), from, n); } extern long strncpy_from_user(char *dest, const char __user *src, long count); @@ -314,7 +362,7 @@ unsigned long __must_check clear_user(void __user *to, unsigned long n) { might_fault(); return access_ok(to, n) ? - __clear_user(to, n) : n; + __clear_user(untagged_addr(to), n) : n; } #define __get_kernel_nofault(dst, src, type, err_label) \ diff --git a/arch/riscv/kernel/process.c b/arch/riscv/kernel/process.c index 1280a7c4a412..f4d8e5c3bb84 100644 --- a/arch/riscv/kernel/process.c +++ b/arch/riscv/kernel/process.c @@ -203,6 +203,10 @@ int copy_thread(struct task_struct *p, const struct kernel_clone_args *args) unsigned long tls = args->tls; struct pt_regs *childregs = task_pt_regs(p); + /* Ensure all threads in this mm have the same pointer masking mode. */ + if (IS_ENABLED(CONFIG_RISCV_ISA_SUPM) && p->mm && (clone_flags & CLONE_VM)) + set_bit(MM_CONTEXT_LOCK_PMLEN, &p->mm->context.flags); + memset(&p->thread.s, 0, sizeof(p->thread.s)); /* p->thread holds context to be restored by __switch_to() */ @@ -248,10 +252,16 @@ enum { static bool have_user_pmlen_7; static bool have_user_pmlen_16; +/* + * Control the relaxed ABI allowing tagged user addresses into the kernel. + */ +static unsigned int tagged_addr_disabled; + long set_tagged_addr_ctrl(struct task_struct *task, unsigned long arg) { - unsigned long valid_mask = PR_PMLEN_MASK; + unsigned long valid_mask = PR_PMLEN_MASK | PR_TAGGED_ADDR_ENABLE; struct thread_info *ti = task_thread_info(task); + struct mm_struct *mm = task->mm; unsigned long pmm; u8 pmlen; @@ -266,16 +276,41 @@ long set_tagged_addr_ctrl(struct task_struct *task, unsigned long arg) * in case choosing a larger PMLEN has a performance impact. */ pmlen = FIELD_GET(PR_PMLEN_MASK, arg); - if (pmlen == PMLEN_0) + if (pmlen == PMLEN_0) { pmm = ENVCFG_PMM_PMLEN_0; - else if (pmlen <= PMLEN_7 && have_user_pmlen_7) + } else if (pmlen <= PMLEN_7 && have_user_pmlen_7) { + pmlen = PMLEN_7; pmm = ENVCFG_PMM_PMLEN_7; - else if (pmlen <= PMLEN_16 && have_user_pmlen_16) + } else if (pmlen <= PMLEN_16 && have_user_pmlen_16) { + pmlen = PMLEN_16; pmm = ENVCFG_PMM_PMLEN_16; - else + } else { return -EINVAL; + } + + /* + * Do not allow the enabling of the tagged address ABI if globally + * disabled via sysctl abi.tagged_addr_disabled, if pointer masking + * is disabled for userspace. + */ + if (arg & PR_TAGGED_ADDR_ENABLE && (tagged_addr_disabled || !pmlen)) + return -EINVAL; + + if (!(arg & PR_TAGGED_ADDR_ENABLE)) + pmlen = PMLEN_0; + + if (mmap_write_lock_killable(mm)) + return -EINTR; + + if (test_bit(MM_CONTEXT_LOCK_PMLEN, &mm->context.flags) && mm->context.pmlen != pmlen) { + mmap_write_unlock(mm); + return -EBUSY; + } envcfg_update_bits(task, ENVCFG_PMM, pmm); + mm->context.pmlen = pmlen; + + mmap_write_unlock(mm); return 0; } @@ -288,6 +323,10 @@ long get_tagged_addr_ctrl(struct task_struct *task) if (is_compat_thread(ti)) return -EINVAL; + /* + * The mm context's pmlen is set only when the tagged address ABI is + * enabled, so the effective PMLEN must be extracted from envcfg.PMM. + */ switch (task->thread.envcfg & ENVCFG_PMM) { case ENVCFG_PMM_PMLEN_7: ret = FIELD_PREP(PR_PMLEN_MASK, PMLEN_7); @@ -297,6 +336,9 @@ long get_tagged_addr_ctrl(struct task_struct *task) break; } + if (task->mm->context.pmlen) + ret |= PR_TAGGED_ADDR_ENABLE; + return ret; } @@ -306,6 +348,24 @@ static bool try_to_set_pmm(unsigned long value) return (csr_read_clear(CSR_ENVCFG, ENVCFG_PMM) & ENVCFG_PMM) == value; } +/* + * Global sysctl to disable the tagged user addresses support. This control + * only prevents the tagged address ABI enabling via prctl() and does not + * disable it for tasks that already opted in to the relaxed ABI. + */ + +static struct ctl_table tagged_addr_sysctl_table[] = { + { + .procname = "tagged_addr_disabled", + .mode = 0644, + .data = &tagged_addr_disabled, + .maxlen = sizeof(int), + .proc_handler = proc_dointvec_minmax, + .extra1 = SYSCTL_ZERO, + .extra2 = SYSCTL_ONE, + }, +}; + static int __init tagged_addr_init(void) { if (!riscv_has_extension_unlikely(RISCV_ISA_EXT_SUPM)) @@ -319,6 +379,9 @@ static int __init tagged_addr_init(void) have_user_pmlen_7 = try_to_set_pmm(ENVCFG_PMM_PMLEN_7); have_user_pmlen_16 = try_to_set_pmm(ENVCFG_PMM_PMLEN_16); + if (!register_sysctl("abi", tagged_addr_sysctl_table)) + return -EINVAL; + return 0; } core_initcall(tagged_addr_init);
When pointer masking is enabled for userspace, the kernel can accept tagged pointers as arguments to some system calls. Allow this by untagging the pointers in access_ok() and the uaccess routines. The uaccess routines must peform untagging in software because U-mode and S-mode have entirely separate pointer masking configurations. In fact, hardware may not even implement pointer masking for S-mode. Since the number of tag bits is variable, untagged_addr_remote() needs to know what PMLEN to use for the remote mm. Therefore, the pointer masking mode must be the same for all threads sharing an mm. Enforce this with a lock flag in the mm context, as x86 does for LAM. The flag gets reset in init_new_context() during fork(), as the new mm is no longer multithreaded. Signed-off-by: Samuel Holland <samuel.holland@sifive.com> --- Changes in v3: - Use IS_ENABLED instead of #ifdef when possible - Implement mm_untag_mask() - Remove pmlen from struct thread_info (now only in mm_context_t) Changes in v2: - Implement untagged_addr_remote() - Restrict PMLEN changes once a process is multithreaded arch/riscv/include/asm/mmu.h | 7 +++ arch/riscv/include/asm/mmu_context.h | 13 +++++ arch/riscv/include/asm/uaccess.h | 58 ++++++++++++++++++++-- arch/riscv/kernel/process.c | 73 ++++++++++++++++++++++++++-- 4 files changed, 141 insertions(+), 10 deletions(-)