| Message ID | 20210707181506.30489-16-brijesh.singh@amd.com (mailing list archive) |
|---|---|
| State | New |
| Headers | show |
| Series | Add AMD Secure Nested Paging (SEV-SNP) Guest Support | expand |
On Wed, Jul 07, 2021 at 01:14:45PM -0500, Brijesh Singh wrote: > +struct __packed psc_hdr { > + u16 cur_entry; > + u16 end_entry; > + u32 reserved; > +}; > + > +struct __packed psc_entry { > + u64 cur_page : 12, > + gfn : 40, > + operation : 4, > + pagesize : 1, > + reserved : 7; > +}; > + > +struct __packed snp_psc_desc { > + struct psc_hdr hdr; > + struct psc_entry entries[VMGEXIT_PSC_MAX_ENTRY]; > +}; The majority of kernel code puts __packed after the struct definition, let's put it there too pls, out of the way. ... > +static int vmgexit_psc(struct snp_psc_desc *desc) > +{ > + int cur_entry, end_entry, ret; > + struct snp_psc_desc *data; > + struct ghcb_state state; > + struct ghcb *ghcb; > + struct psc_hdr *hdr; > + unsigned long flags; > + > + local_irq_save(flags); > + > + ghcb = __sev_get_ghcb(&state); > + if (unlikely(!ghcb)) > + panic("SEV-SNP: Failed to get GHCB\n"); > + > + /* Copy the input desc into GHCB shared buffer */ > + data = (struct snp_psc_desc *)ghcb->shared_buffer; > + memcpy(ghcb->shared_buffer, desc, sizeof(*desc)); > + > + hdr = &data->hdr; > + cur_entry = hdr->cur_entry; > + end_entry = hdr->end_entry; > + > + /* > + * As per the GHCB specification, the hypervisor can resume the guest > + * before processing all the entries. Checks whether all the entries > + * are processed. If not, then keep retrying. > + * > + * The stragtegy here is to wait for the hypervisor to change the page > + * state in the RMP table before guest access the memory pages. If the > + * page state was not successful, then later memory access will result > + * in the crash. > + */ > + while (hdr->cur_entry <= hdr->end_entry) { > + ghcb_set_sw_scratch(ghcb, (u64)__pa(data)); > + > + ret = sev_es_ghcb_hv_call(ghcb, NULL, SVM_VMGEXIT_PSC, 0, 0); > + > + /* > + * Page State Change VMGEXIT can pass error code through > + * exit_info_2. > + */ > + if (WARN(ret || ghcb->save.sw_exit_info_2, > + "SEV-SNP: page state change failed ret=%d exit_info_2=%llx\n", > + ret, ghcb->save.sw_exit_info_2)) > + return 1; Yikes, you return here and below with interrupts disabled. All your returns need to be "goto out;" instead where you do out: __sev_put_ghcb(&state); local_irq_restore(flags); Yap, you very likely need to put the GHCB too. > + /* > + * Lets do some sanity check that entry processing is not going > + * backward. This will happen only if hypervisor is tricking us. > + */ > + if (WARN((hdr->end_entry > end_entry) || (cur_entry > hdr->cur_entry), > + "SEV-SNP: page state change processing going backward, end_entry " > + "(expected %d got %d) cur_entry (expected %d got %d)\n", > + end_entry, hdr->end_entry, cur_entry, hdr->cur_entry)) > + return 1; WARNING: quoted string split across lines #293: FILE: arch/x86/kernel/sev.c:750: + "SEV-SNP: page state change processing going backward, end_entry " + "(expected %d got %d) cur_entry (expected %d got %d)\n", If you're wondering what to do, yes, you can really stretch that string and shorten it too: if (WARN((hdr->end_entry > end_entry) || (cur_entry > hdr->cur_entry), "SEV-SNP: PSC processing going backwards, end_entry %d (got %d) cur_entry: %d (got %d)\n", end_entry, hdr->end_entry, cur_entry, hdr->cur_entry)) return 1; so that it fits on a single line and grepping can find it. > + /* Lets verify that reserved bit is not set in the header*/ > + if (WARN(hdr->reserved, "Reserved bit is set in the PSC header\n")) psc_entry has a ->reserved field too and since we're iterating over the entries... > + return 1; > + } > + > + __sev_put_ghcb(&state); > + local_irq_restore(flags); > + > + return 0; > +} > + > +static void __set_page_state(struct snp_psc_desc *data, unsigned long vaddr, > + unsigned long vaddr_end, int op) > +{ > + struct psc_hdr *hdr; > + struct psc_entry *e; > + unsigned long pfn; > + int i; > + > + hdr = &data->hdr; > + e = data->entries; > + > + memset(data, 0, sizeof(*data)); > + i = 0; > + > + while (vaddr < vaddr_end) { > + if (is_vmalloc_addr((void *)vaddr)) > + pfn = vmalloc_to_pfn((void *)vaddr); > + else > + pfn = __pa(vaddr) >> PAGE_SHIFT; > + > + e->gfn = pfn; > + e->operation = op; > + hdr->end_entry = i; > + > + /* > + * The GHCB specification provides the flexibility to > + * use either 4K or 2MB page size in the RMP table. > + * The current SNP support does not keep track of the > + * page size used in the RMP table. To avoid the > + * overlap request, use the 4K page size in the RMP > + * table. > + */ > + e->pagesize = RMP_PG_SIZE_4K; > + > + vaddr = vaddr + PAGE_SIZE; > + e++; > + i++; > + } > + > + /* Terminate the guest on page state change failure. */ That comment is kinda obvious :) > + if (vmgexit_psc(data)) > + sev_es_terminate(1, GHCB_TERM_PSC); > +} > + > +static void set_page_state(unsigned long vaddr, unsigned int npages, int op) > +{ > + unsigned long vaddr_end, next_vaddr; > + struct snp_psc_desc *desc; > + > + vaddr = vaddr & PAGE_MASK; > + vaddr_end = vaddr + (npages << PAGE_SHIFT); > + > + desc = kmalloc(sizeof(*desc), GFP_KERNEL_ACCOUNT); kzalloc() so that you don't have to memset() later in __set_page_state(). > + if (!desc) > + panic("failed to allocate memory"); Make that error message more distinctive so that *if* it happens, one can pinpoint the place in the code where the panic comes from. > + while (vaddr < vaddr_end) { > + /* > + * Calculate the last vaddr that can be fit in one > + * struct snp_psc_desc. > + */ > + next_vaddr = min_t(unsigned long, vaddr_end, > + (VMGEXIT_PSC_MAX_ENTRY * PAGE_SIZE) + vaddr); > + > + __set_page_state(desc, vaddr, next_vaddr, op); > + > + vaddr = next_vaddr; > + } > + > + kfree(desc); > +} > +
On 8/17/21 12:27 PM, Borislav Petkov wrote: > > The majority of kernel code puts __packed after the struct definition, > let's put it there too pls, out of the way. > > ... Noted. >> + if (WARN(ret || ghcb->save.sw_exit_info_2, >> + "SEV-SNP: page state change failed ret=%d exit_info_2=%llx\n", >> + ret, ghcb->save.sw_exit_info_2)) >> + return 1; > > Yikes, you return here and below with interrupts disabled. > > All your returns need to be "goto out;" instead where you do > > out: > __sev_put_ghcb(&state); > local_irq_restore(flags); > > Yap, you very likely need to put the GHCB too. > Sure, let me revisit this code to fix those path. >> + /* >> + * Lets do some sanity check that entry processing is not going >> + * backward. This will happen only if hypervisor is tricking us. >> + */ >> + if (WARN((hdr->end_entry > end_entry) || (cur_entry > hdr->cur_entry), >> + "SEV-SNP: page state change processing going backward, end_entry " >> + "(expected %d got %d) cur_entry (expected %d got %d)\n", >> + end_entry, hdr->end_entry, cur_entry, hdr->cur_entry)) >> + return 1; > > WARNING: quoted string split across lines > #293: FILE: arch/x86/kernel/sev.c:750: > + "SEV-SNP: page state change processing going backward, end_entry " > + "(expected %d got %d) cur_entry (expected %d got %d)\n", > > If you're wondering what to do, yes, you can really stretch that string > and shorten it too: Okay. > > if (WARN((hdr->end_entry > end_entry) || (cur_entry > hdr->cur_entry), > "SEV-SNP: PSC processing going backwards, end_entry %d (got %d) cur_entry: %d (got %d)\n", > end_entry, hdr->end_entry, cur_entry, hdr->cur_entry)) > return 1; > > so that it fits on a single line and grepping can find it. > Noted. >> + /* Lets verify that reserved bit is not set in the header*/ >> + if (WARN(hdr->reserved, "Reserved bit is set in the PSC header\n")) > > psc_entry has a ->reserved field too and since we're iterating over the > entries... > Sure I can add that check. >> + >> + desc = kmalloc(sizeof(*desc), GFP_KERNEL_ACCOUNT); > > kzalloc() so that you don't have to memset() later in > __set_page_state(). Depending on the size, the __set_page_state() can be call multiple times so it should clear the desc memory before filling it. > >> + if (!desc) >> + panic("failed to allocate memory"); > > Make that error message more distinctive so that *if* it happens, one > can pinpoint the place in the code where the panic comes from. > Now I am running checkpatch and notice that it complain about the message too. I can add a BUG() or WARN() to get the stack trace before the crashing. >> + while (vaddr < vaddr_end) { >> + /* >> + * Calculate the last vaddr that can be fit in one >> + * struct snp_psc_desc. >> + */ >> + next_vaddr = min_t(unsigned long, vaddr_end, >> + (VMGEXIT_PSC_MAX_ENTRY * PAGE_SIZE) + vaddr); >> + >> + __set_page_state(desc, vaddr, next_vaddr, op); >> + >> + vaddr = next_vaddr; >> + } >> + >> + kfree(desc); >> +} >> + >
On Tue, Aug 17, 2021 at 01:07:40PM -0500, Brijesh Singh wrote: > > > + if (!desc) > > > + panic("failed to allocate memory"); > > > > Make that error message more distinctive so that *if* it happens, one > > can pinpoint the place in the code where the panic comes from. > > > > Now I am running checkpatch and notice that it complain about the message > too. I can add a BUG() or WARN() to get the stack trace before the crashing. checkpatch complains because there's a kmalloc before it and if it fails, the mm core will issue a warning so there's no need for a warning here. But in this case, you want to panic and checkpatch doesn't see that so you can ignore it here and leave the panic message but make it more distinctive so one can find it by grepping. IOW, something like if (!desc) panic("SEV-SNP: Failed to allocame memory for PSC descriptor"); Thx.
On 8/17/21 1:17 PM, Borislav Petkov wrote: > On Tue, Aug 17, 2021 at 01:07:40PM -0500, Brijesh Singh wrote: >>>> + if (!desc) >>>> + panic("failed to allocate memory"); >>> >>> Make that error message more distinctive so that *if* it happens, one >>> can pinpoint the place in the code where the panic comes from. >>> >> >> Now I am running checkpatch and notice that it complain about the message >> too. I can add a BUG() or WARN() to get the stack trace before the crashing. > > checkpatch complains because there's a kmalloc before it and if it > fails, the mm core will issue a warning so there's no need for a warning > here. > > But in this case, you want to panic and checkpatch doesn't see that so > you can ignore it here and leave the panic message but make it more > distinctive so one can find it by grepping. IOW, something like > > if (!desc) > panic("SEV-SNP: Failed to allocame memory for PSC descriptor"); > Got it, I will update the message accordingly. thanks
Hi Boris, On 8/17/21 12:27 PM, Borislav Petkov wrote: > >> + /* Lets verify that reserved bit is not set in the header*/ >> + if (WARN(hdr->reserved, "Reserved bit is set in the PSC header\n")) > > psc_entry has a ->reserved field too and since we're iterating over the > entries... > I am not seeing any strong reason to sanity check the reserved bit in the psc_entry. The fields in the psc_entry are input from guest to the hypervisor. The hypervisor cannot trick a guest by changing anything in the psc_entry because guest does not read the hypervisor filled value. I am okay with the psc_hdr because we need to read the current and end entry after the PSC completes to determine whether it was successful and sanity checking PSC header makes much more sense. Let me know if you are okay with it ? thanks
On Tue, Aug 17, 2021 at 03:34:41PM -0500, Brijesh Singh wrote: > I am not seeing any strong reason to sanity check the reserved bit in the > psc_entry. The fields in the psc_entry are input from guest to the > hypervisor. The hypervisor cannot trick a guest by changing anything in the > psc_entry because guest does not read the hypervisor filled value. I am okay > with the psc_hdr because we need to read the current and end entry after the > PSC completes to determine whether it was successful and sanity checking PSC > header makes much more sense. Let me know if you are okay with it ? Ok, fair enough. Thx.
diff --git a/arch/x86/include/asm/sev-common.h b/arch/x86/include/asm/sev-common.h index b19d8d301f5d..2277c8085b13 100644 --- a/arch/x86/include/asm/sev-common.h +++ b/arch/x86/include/asm/sev-common.h @@ -60,6 +60,8 @@ #define GHCB_MSR_PSC_REQ 0x014 #define SNP_PAGE_STATE_PRIVATE 1 #define SNP_PAGE_STATE_SHARED 2 +#define SNP_PAGE_STATE_PSMASH 3 +#define SNP_PAGE_STATE_UNSMASH 4 #define GHCB_MSR_PSC_GFN_POS 12 #define GHCB_MSR_PSC_GFN_MASK GENMASK_ULL(39, 0) #define GHCB_MSR_PSC_OP_POS 52 @@ -84,6 +86,28 @@ #define GHCB_HV_FT_SNP BIT_ULL(0) +/* SNP Page State Change NAE event */ +#define VMGEXIT_PSC_MAX_ENTRY 253 + +struct __packed psc_hdr { + u16 cur_entry; + u16 end_entry; + u32 reserved; +}; + +struct __packed psc_entry { + u64 cur_page : 12, + gfn : 40, + operation : 4, + pagesize : 1, + reserved : 7; +}; + +struct __packed snp_psc_desc { + struct psc_hdr hdr; + struct psc_entry entries[VMGEXIT_PSC_MAX_ENTRY]; +}; + #define GHCB_MSR_TERM_REQ 0x100 #define GHCB_MSR_TERM_REASON_SET_POS 12 #define GHCB_MSR_TERM_REASON_SET_MASK 0xf diff --git a/arch/x86/include/asm/sev.h b/arch/x86/include/asm/sev.h index 9a676fb0929d..2385651c810e 100644 --- a/arch/x86/include/asm/sev.h +++ b/arch/x86/include/asm/sev.h @@ -109,6 +109,8 @@ void __init early_snp_set_memory_private(unsigned long vaddr, unsigned long padd void __init early_snp_set_memory_shared(unsigned long vaddr, unsigned long paddr, unsigned int npages); void __init snp_prep_memory(unsigned long paddr, unsigned int sz, int op); +void snp_set_memory_shared(unsigned long vaddr, unsigned int npages); +void snp_set_memory_private(unsigned long vaddr, unsigned int npages); #else static inline void sev_es_ist_enter(struct pt_regs *regs) { } static inline void sev_es_ist_exit(void) { } @@ -121,6 +123,8 @@ early_snp_set_memory_private(unsigned long vaddr, unsigned long paddr, unsigned static inline void __init early_snp_set_memory_shared(unsigned long vaddr, unsigned long paddr, unsigned int npages) { } static inline void __init snp_prep_memory(unsigned long paddr, unsigned int sz, int op) { } +static inline void snp_set_memory_shared(unsigned long vaddr, unsigned int npages) { } +static inline void snp_set_memory_private(unsigned long vaddr, unsigned int npages) { } #endif #endif diff --git a/arch/x86/include/uapi/asm/svm.h b/arch/x86/include/uapi/asm/svm.h index 7fbc311e2de1..f7f65febff70 100644 --- a/arch/x86/include/uapi/asm/svm.h +++ b/arch/x86/include/uapi/asm/svm.h @@ -108,6 +108,7 @@ #define SVM_VMGEXIT_AP_JUMP_TABLE 0x80000005 #define SVM_VMGEXIT_SET_AP_JUMP_TABLE 0 #define SVM_VMGEXIT_GET_AP_JUMP_TABLE 1 +#define SVM_VMGEXIT_PSC 0x80000010 #define SVM_VMGEXIT_HYPERVISOR_FEATURES 0x8000fffd #define SVM_VMGEXIT_UNSUPPORTED_EVENT 0x8000ffff @@ -216,6 +217,7 @@ { SVM_VMGEXIT_NMI_COMPLETE, "vmgexit_nmi_complete" }, \ { SVM_VMGEXIT_AP_HLT_LOOP, "vmgexit_ap_hlt_loop" }, \ { SVM_VMGEXIT_AP_JUMP_TABLE, "vmgexit_ap_jump_table" }, \ + { SVM_VMGEXIT_PSC, "vmgexit_page_state_change" }, \ { SVM_VMGEXIT_HYPERVISOR_FEATURES, "vmgexit_hypervisor_feature" }, \ { SVM_EXIT_ERR, "invalid_guest_state" } diff --git a/arch/x86/kernel/sev.c b/arch/x86/kernel/sev.c index 62034879fb3f..5fef7fc46282 100644 --- a/arch/x86/kernel/sev.c +++ b/arch/x86/kernel/sev.c @@ -694,6 +694,166 @@ void __init snp_prep_memory(unsigned long paddr, unsigned int sz, int op) WARN(1, "invalid memory op %d\n", op); } +static int vmgexit_psc(struct snp_psc_desc *desc) +{ + int cur_entry, end_entry, ret; + struct snp_psc_desc *data; + struct ghcb_state state; + struct ghcb *ghcb; + struct psc_hdr *hdr; + unsigned long flags; + + local_irq_save(flags); + + ghcb = __sev_get_ghcb(&state); + if (unlikely(!ghcb)) + panic("SEV-SNP: Failed to get GHCB\n"); + + /* Copy the input desc into GHCB shared buffer */ + data = (struct snp_psc_desc *)ghcb->shared_buffer; + memcpy(ghcb->shared_buffer, desc, sizeof(*desc)); + + hdr = &data->hdr; + cur_entry = hdr->cur_entry; + end_entry = hdr->end_entry; + + /* + * As per the GHCB specification, the hypervisor can resume the guest + * before processing all the entries. Checks whether all the entries + * are processed. If not, then keep retrying. + * + * The stragtegy here is to wait for the hypervisor to change the page + * state in the RMP table before guest access the memory pages. If the + * page state was not successful, then later memory access will result + * in the crash. + */ + while (hdr->cur_entry <= hdr->end_entry) { + ghcb_set_sw_scratch(ghcb, (u64)__pa(data)); + + ret = sev_es_ghcb_hv_call(ghcb, NULL, SVM_VMGEXIT_PSC, 0, 0); + + /* + * Page State Change VMGEXIT can pass error code through + * exit_info_2. + */ + if (WARN(ret || ghcb->save.sw_exit_info_2, + "SEV-SNP: page state change failed ret=%d exit_info_2=%llx\n", + ret, ghcb->save.sw_exit_info_2)) + return 1; + + /* + * Lets do some sanity check that entry processing is not going + * backward. This will happen only if hypervisor is tricking us. + */ + if (WARN((hdr->end_entry > end_entry) || (cur_entry > hdr->cur_entry), + "SEV-SNP: page state change processing going backward, end_entry " + "(expected %d got %d) cur_entry (expected %d got %d)\n", + end_entry, hdr->end_entry, cur_entry, hdr->cur_entry)) + return 1; + + /* Lets verify that reserved bit is not set in the header*/ + if (WARN(hdr->reserved, "Reserved bit is set in the PSC header\n")) + return 1; + } + + __sev_put_ghcb(&state); + local_irq_restore(flags); + + return 0; +} + +static void __set_page_state(struct snp_psc_desc *data, unsigned long vaddr, + unsigned long vaddr_end, int op) +{ + struct psc_hdr *hdr; + struct psc_entry *e; + unsigned long pfn; + int i; + + hdr = &data->hdr; + e = data->entries; + + memset(data, 0, sizeof(*data)); + i = 0; + + while (vaddr < vaddr_end) { + if (is_vmalloc_addr((void *)vaddr)) + pfn = vmalloc_to_pfn((void *)vaddr); + else + pfn = __pa(vaddr) >> PAGE_SHIFT; + + e->gfn = pfn; + e->operation = op; + hdr->end_entry = i; + + /* + * The GHCB specification provides the flexibility to + * use either 4K or 2MB page size in the RMP table. + * The current SNP support does not keep track of the + * page size used in the RMP table. To avoid the + * overlap request, use the 4K page size in the RMP + * table. + */ + e->pagesize = RMP_PG_SIZE_4K; + + vaddr = vaddr + PAGE_SIZE; + e++; + i++; + } + + /* Terminate the guest on page state change failure. */ + if (vmgexit_psc(data)) + sev_es_terminate(1, GHCB_TERM_PSC); +} + +static void set_page_state(unsigned long vaddr, unsigned int npages, int op) +{ + unsigned long vaddr_end, next_vaddr; + struct snp_psc_desc *desc; + + vaddr = vaddr & PAGE_MASK; + vaddr_end = vaddr + (npages << PAGE_SHIFT); + + desc = kmalloc(sizeof(*desc), GFP_KERNEL_ACCOUNT); + if (!desc) + panic("failed to allocate memory"); + + while (vaddr < vaddr_end) { + /* + * Calculate the last vaddr that can be fit in one + * struct snp_psc_desc. + */ + next_vaddr = min_t(unsigned long, vaddr_end, + (VMGEXIT_PSC_MAX_ENTRY * PAGE_SIZE) + vaddr); + + __set_page_state(desc, vaddr, next_vaddr, op); + + vaddr = next_vaddr; + } + + kfree(desc); +} + +void snp_set_memory_shared(unsigned long vaddr, unsigned int npages) +{ + if (!sev_feature_enabled(SEV_SNP)) + return; + + pvalidate_pages(vaddr, npages, 0); + + set_page_state(vaddr, npages, SNP_PAGE_STATE_SHARED); +} + +void snp_set_memory_private(unsigned long vaddr, unsigned int npages) +{ + if (!sev_feature_enabled(SEV_SNP)) + return; + + set_page_state(vaddr, npages, SNP_PAGE_STATE_PRIVATE); + + pvalidate_pages(vaddr, npages, 1); +} + int sev_es_setup_ap_jump_table(struct real_mode_header *rmh) { u16 startup_cs, startup_ip; diff --git a/arch/x86/mm/pat/set_memory.c b/arch/x86/mm/pat/set_memory.c index 156cd235659f..d09df2971d30 100644 --- a/arch/x86/mm/pat/set_memory.c +++ b/arch/x86/mm/pat/set_memory.c @@ -29,6 +29,7 @@ #include <asm/proto.h> #include <asm/memtype.h> #include <asm/set_memory.h> +#include <asm/sev.h> #include "../mm_internal.h" @@ -2009,8 +2010,22 @@ static int __set_memory_enc_dec(unsigned long addr, int numpages, bool enc) */ cpa_flush(&cpa, !this_cpu_has(X86_FEATURE_SME_COHERENT)); + /* + * To maintain the security gurantees of SEV-SNP guest invalidate the memory + * before clearing the encryption attribute. + */ + if (!enc) + snp_set_memory_shared(addr, numpages); + ret = __change_page_attr_set_clr(&cpa, 1); + /* + * Now that memory is mapped encrypted in the page table, validate it + * so that is consistent with the above page state. + */ + if (!ret && enc) + snp_set_memory_private(addr, numpages); + /* * After changing the encryption attribute, we need to flush TLBs again * in case any speculative TLB caching occurred (but no need to flush
The set_memory_{encrypt,decrypt}() are used for changing the pages from decrypted (shared) to encrypted (private) and vice versa. When SEV-SNP is active, the page state transition needs to go through additional steps. If the page is transitioned from shared to private, then perform the following after the encryption attribute is set in the page table: 1. Issue the page state change VMGEXIT to add the memory region in the RMP table. 2. Validate the memory region after the RMP entry is added. To maintain the security guarantees, if the page is transitioned from private to shared, then perform the following before encryption attribute is removed from the page table: 1. Invalidate the page. 2. Issue the page state change VMGEXIT to remove the page from RMP table. To change the page state in the RMP table, use the Page State Change VMGEXIT defined in the GHCB specification. Signed-off-by: Brijesh Singh <brijesh.singh@amd.com> --- arch/x86/include/asm/sev-common.h | 24 +++++ arch/x86/include/asm/sev.h | 4 + arch/x86/include/uapi/asm/svm.h | 2 + arch/x86/kernel/sev.c | 160 ++++++++++++++++++++++++++++++ arch/x86/mm/pat/set_memory.c | 15 +++ 5 files changed, 205 insertions(+)