| Message ID | 1410238199-956-1-git-send-email-takahiro.akashi@linaro.org (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
Hi Akashi, On Tue, Sep 09, 2014 at 05:49:59AM +0100, AKASHI Takahiro wrote: > BUG_ON() in audit_syscall_entry() will be hit if user issues syscall(-1) > while syscall auditing is enabled (that is, by starting auditd). [...] > diff --git a/arch/arm/include/asm/traps.h b/arch/arm/include/asm/traps.h > index f555bb3..de01145 100644 > --- a/arch/arm/include/asm/traps.h > +++ b/arch/arm/include/asm/traps.h > @@ -49,6 +49,7 @@ static inline int in_exception_text(unsigned long ptr) > extern void __init early_trap_init(void *); > extern void dump_backtrace_entry(unsigned long where, unsigned long from, unsigned long frame); > extern void ptrace_break(struct task_struct *tsk, struct pt_regs *regs); > +extern int arm_syscall(int no, struct pt_regs *regs); > > extern void *vectors_page; > > diff --git a/arch/arm/kernel/entry-common.S b/arch/arm/kernel/entry-common.S > index e52fe5a..28d3931 100644 > --- a/arch/arm/kernel/entry-common.S > +++ b/arch/arm/kernel/entry-common.S > @@ -426,7 +426,6 @@ ENTRY(vector_swi) > local_restart: > ldr r10, [tsk, #TI_FLAGS] @ check for syscall tracing > stmdb sp!, {r4, r5} @ push fifth and sixth args > - You don't need this cosmetic change. > tst r10, #_TIF_SYSCALL_WORK @ are we tracing syscalls? > bne __sys_trace > > @@ -476,10 +475,11 @@ __sys_trace: > cmp scno, #-1 @ skip the syscall? > bne 2b > add sp, sp, #S_OFF @ restore stack > - b ret_slow_syscall > + b __sys_trace_return_skipped Can't you just remove the add as well, them fall-through here? > > __sys_trace_return: > str r0, [sp, #S_R0 + S_OFF]! @ save returned r0 > +__sys_trace_return_skipped: > mov r0, sp > bl syscall_trace_exit > b ret_slow_syscall > diff --git a/arch/arm/kernel/ptrace.c b/arch/arm/kernel/ptrace.c > index 0c27ed6..68b42cd 100644 > --- a/arch/arm/kernel/ptrace.c > +++ b/arch/arm/kernel/ptrace.c > @@ -930,7 +930,9 @@ static void tracehook_report_syscall(struct pt_regs *regs, > > asmlinkage int syscall_trace_enter(struct pt_regs *regs, int scno) > { > - current_thread_info()->syscall = scno; > + int orig_scno; > + > + current_thread_info()->syscall = orig_scno = scno; > > /* Do the secure computing check first; failures should be fast. */ > if (secure_computing(scno) == -1) > @@ -941,31 +943,40 @@ asmlinkage int syscall_trace_enter(struct pt_regs *regs, int scno) > > scno = current_thread_info()->syscall; > > - if (test_thread_flag(TIF_SYSCALL_TRACEPOINT)) > - trace_sys_enter(regs, scno); > + if (scno >= 0 && scno < NR_syscalls) { Is this supposed to work for OABI? If so, better use __NR_SYSCALL_BASE. > + if (test_thread_flag(TIF_SYSCALL_TRACEPOINT)) > + trace_sys_enter(regs, scno); > + > + audit_syscall_entry(AUDIT_ARCH_ARM, scno, > + regs->ARM_r0, regs->ARM_r1, > + regs->ARM_r2, regs->ARM_r3); > + } > > - audit_syscall_entry(AUDIT_ARCH_ARM, scno, regs->ARM_r0, regs->ARM_r1, > - regs->ARM_r2, regs->ARM_r3); > + /* user-issued syscall of -1 */ > + if (scno == -1 && orig_scno == -1) Make this an else if, for clarity? > + arm_syscall(scno, regs); Doesn't this always result in bad_syscall being called, which sends a SIGILL to the task? Shouldn't we simply return -ENOSYS instead? You could do that in the assembly code. > return scno; > } > > asmlinkage void syscall_trace_exit(struct pt_regs *regs) > { > - /* > - * Audit the syscall before anything else, as a debugger may > - * come in and change the current registers. > - */ > - audit_syscall_exit(regs); > + if (current_thread_info()->syscall < NR_syscalls) { Again, not going to work for OABI. Will
Will, Sorry for not responding quickly. On 09/11/2014 09:37 AM, Will Deacon wrote: > Hi Akashi, > > On Tue, Sep 09, 2014 at 05:49:59AM +0100, AKASHI Takahiro wrote: >> BUG_ON() in audit_syscall_entry() will be hit if user issues syscall(-1) >> while syscall auditing is enabled (that is, by starting auditd). > > [...] > >> diff --git a/arch/arm/include/asm/traps.h b/arch/arm/include/asm/traps.h >> index f555bb3..de01145 100644 >> --- a/arch/arm/include/asm/traps.h >> +++ b/arch/arm/include/asm/traps.h >> @@ -49,6 +49,7 @@ static inline int in_exception_text(unsigned long ptr) >> extern void __init early_trap_init(void *); >> extern void dump_backtrace_entry(unsigned long where, unsigned long from, unsigned long frame); >> extern void ptrace_break(struct task_struct *tsk, struct pt_regs *regs); >> +extern int arm_syscall(int no, struct pt_regs *regs); >> >> extern void *vectors_page; >> >> diff --git a/arch/arm/kernel/entry-common.S b/arch/arm/kernel/entry-common.S >> index e52fe5a..28d3931 100644 >> --- a/arch/arm/kernel/entry-common.S >> +++ b/arch/arm/kernel/entry-common.S >> @@ -426,7 +426,6 @@ ENTRY(vector_swi) >> local_restart: >> ldr r10, [tsk, #TI_FLAGS] @ check for syscall tracing >> stmdb sp!, {r4, r5} @ push fifth and sixth args >> - > > You don't need this cosmetic change. Typo. I will fix it. >> tst r10, #_TIF_SYSCALL_WORK @ are we tracing syscalls? >> bne __sys_trace >> >> @@ -476,10 +475,11 @@ __sys_trace: >> cmp scno, #-1 @ skip the syscall? >> bne 2b >> add sp, sp, #S_OFF @ restore stack >> - b ret_slow_syscall >> + b __sys_trace_return_skipped > > Can't you just remove the add as well, them fall-through here? I'm afraid that we can't remove this branch because we don't want to override a value of r0 in regs which a tracer may have already changed while skipping a syscall. >> >> __sys_trace_return: >> str r0, [sp, #S_R0 + S_OFF]! @ save returned r0 >> +__sys_trace_return_skipped: >> mov r0, sp >> bl syscall_trace_exit >> b ret_slow_syscall >> diff --git a/arch/arm/kernel/ptrace.c b/arch/arm/kernel/ptrace.c >> index 0c27ed6..68b42cd 100644 >> --- a/arch/arm/kernel/ptrace.c >> +++ b/arch/arm/kernel/ptrace.c >> @@ -930,7 +930,9 @@ static void tracehook_report_syscall(struct pt_regs *regs, >> >> asmlinkage int syscall_trace_enter(struct pt_regs *regs, int scno) >> { >> - current_thread_info()->syscall = scno; >> + int orig_scno; >> + >> + current_thread_info()->syscall = orig_scno = scno; >> >> /* Do the secure computing check first; failures should be fast. */ >> if (secure_computing(scno) == -1) >> @@ -941,31 +943,40 @@ asmlinkage int syscall_trace_enter(struct pt_regs *regs, int scno) >> >> scno = current_thread_info()->syscall; >> >> - if (test_thread_flag(TIF_SYSCALL_TRACEPOINT)) >> - trace_sys_enter(regs, scno); >> + if (scno >= 0 && scno < NR_syscalls) { > > Is this supposed to work for OABI? If so, better use __NR_SYSCALL_BASE. Good point. I'm not quite sure how it works for OABI, but looking into entry-comon.S, there is some code: > #if defined(CONFIG_OABI_COMPAT) > bics r10, r10, #0xff000000 > eorne scno, r10, #__NR_OABI_SYSCALL_BASE > ldrne tbl, =sys_oabi_call_table > #elif !defined(CONFIG_AEABI) > bic scno, scno, #0xff000000 @ mask off SWI op-code > eor scno, scno, #__NR_SYSCALL_BASE @ check OS number > #endif > > local_restart: It seems to me that scno, actually r7 in regs, is already offset. >> + if (test_thread_flag(TIF_SYSCALL_TRACEPOINT)) >> + trace_sys_enter(regs, scno); >> + >> + audit_syscall_entry(AUDIT_ARCH_ARM, scno, >> + regs->ARM_r0, regs->ARM_r1, >> + regs->ARM_r2, regs->ARM_r3); >> + } >> >> - audit_syscall_entry(AUDIT_ARCH_ARM, scno, regs->ARM_r0, regs->ARM_r1, >> - regs->ARM_r2, regs->ARM_r3); >> + /* user-issued syscall of -1 */ >> + if (scno == -1 && orig_scno == -1) > > Make this an else if, for clarity? Sure. I will fix it. >> + arm_syscall(scno, regs); > > Doesn't this always result in bad_syscall being called, which sends a SIGILL > to the task? Shouldn't we simply return -ENOSYS instead? You could do that > in the assembly code. I meant so (that is, resulting in bad_syscall). As I mentioned earlier, a task calling syscall(-1, or whatever native value) is always signaled on arm. Meanwhile, whether it is intended or not, this behavior is not simulated in the current arm64 compat syscalls. >> return scno; >> } >> >> asmlinkage void syscall_trace_exit(struct pt_regs *regs) >> { >> - /* >> - * Audit the syscall before anything else, as a debugger may >> - * come in and change the current registers. >> - */ >> - audit_syscall_exit(regs); >> + if (current_thread_info()->syscall < NR_syscalls) { > > Again, not going to work for OABI. The same comment above. Thanks, -Takahiro AKASHI > Will >
diff --git a/arch/arm/include/asm/traps.h b/arch/arm/include/asm/traps.h index f555bb3..de01145 100644 --- a/arch/arm/include/asm/traps.h +++ b/arch/arm/include/asm/traps.h @@ -49,6 +49,7 @@ static inline int in_exception_text(unsigned long ptr) extern void __init early_trap_init(void *); extern void dump_backtrace_entry(unsigned long where, unsigned long from, unsigned long frame); extern void ptrace_break(struct task_struct *tsk, struct pt_regs *regs); +extern int arm_syscall(int no, struct pt_regs *regs); extern void *vectors_page; diff --git a/arch/arm/kernel/entry-common.S b/arch/arm/kernel/entry-common.S index e52fe5a..28d3931 100644 --- a/arch/arm/kernel/entry-common.S +++ b/arch/arm/kernel/entry-common.S @@ -426,7 +426,6 @@ ENTRY(vector_swi) local_restart: ldr r10, [tsk, #TI_FLAGS] @ check for syscall tracing stmdb sp!, {r4, r5} @ push fifth and sixth args - tst r10, #_TIF_SYSCALL_WORK @ are we tracing syscalls? bne __sys_trace @@ -476,10 +475,11 @@ __sys_trace: cmp scno, #-1 @ skip the syscall? bne 2b add sp, sp, #S_OFF @ restore stack - b ret_slow_syscall + b __sys_trace_return_skipped __sys_trace_return: str r0, [sp, #S_R0 + S_OFF]! @ save returned r0 +__sys_trace_return_skipped: mov r0, sp bl syscall_trace_exit b ret_slow_syscall diff --git a/arch/arm/kernel/ptrace.c b/arch/arm/kernel/ptrace.c index 0c27ed6..68b42cd 100644 --- a/arch/arm/kernel/ptrace.c +++ b/arch/arm/kernel/ptrace.c @@ -930,7 +930,9 @@ static void tracehook_report_syscall(struct pt_regs *regs, asmlinkage int syscall_trace_enter(struct pt_regs *regs, int scno) { - current_thread_info()->syscall = scno; + int orig_scno; + + current_thread_info()->syscall = orig_scno = scno; /* Do the secure computing check first; failures should be fast. */ if (secure_computing(scno) == -1) @@ -941,31 +943,40 @@ asmlinkage int syscall_trace_enter(struct pt_regs *regs, int scno) scno = current_thread_info()->syscall; - if (test_thread_flag(TIF_SYSCALL_TRACEPOINT)) - trace_sys_enter(regs, scno); + if (scno >= 0 && scno < NR_syscalls) { + if (test_thread_flag(TIF_SYSCALL_TRACEPOINT)) + trace_sys_enter(regs, scno); + + audit_syscall_entry(AUDIT_ARCH_ARM, scno, + regs->ARM_r0, regs->ARM_r1, + regs->ARM_r2, regs->ARM_r3); + } - audit_syscall_entry(AUDIT_ARCH_ARM, scno, regs->ARM_r0, regs->ARM_r1, - regs->ARM_r2, regs->ARM_r3); + /* user-issued syscall of -1 */ + if (scno == -1 && orig_scno == -1) + arm_syscall(scno, regs); return scno; } asmlinkage void syscall_trace_exit(struct pt_regs *regs) { - /* - * Audit the syscall before anything else, as a debugger may - * come in and change the current registers. - */ - audit_syscall_exit(regs); + if (current_thread_info()->syscall < NR_syscalls) { + /* + * Audit the syscall before anything else, as a debugger may + * come in and change the current registers. + */ + audit_syscall_exit(regs); - /* - * Note that we haven't updated the ->syscall field for the - * current thread. This isn't a problem because it will have - * been set on syscall entry and there hasn't been an opportunity - * for a PTRACE_SET_SYSCALL since then. - */ - if (test_thread_flag(TIF_SYSCALL_TRACEPOINT)) - trace_sys_exit(regs, regs_return_value(regs)); + /* + * Note that we haven't updated the ->syscall field for the + * current thread. This isn't a problem because it will have + * been set on syscall entry and there hasn't been + * an opportunity for a PTRACE_SET_SYSCALL since then. + */ + if (test_thread_flag(TIF_SYSCALL_TRACEPOINT)) + trace_sys_exit(regs, regs_return_value(regs)); + } if (test_thread_flag(TIF_SYSCALL_TRACE)) tracehook_report_syscall(regs, PTRACE_SYSCALL_EXIT);
BUG_ON() in audit_syscall_entry() will be hit if user issues syscall(-1) while syscall auditing is enabled (that is, by starting auditd). ------------[ cut here ]------------ kernel BUG at /home/akashi/arm/armv7/linux/kernel/auditsc.c:1534! Internal error: Oops - BUG: 0 [#1] SMP ARM Modules linked in: CPU: 0 PID: 61 Comm: syscall_arm Not tainted 3.17.0-rc4 #60 task: ea0c4380 ti: ea48e000 task.ti: ea48e000 PC is at __audit_syscall_entry+0xe4/0x110 LR is at 0xea0c4380 pc : [<c02b2ae8>] lr : [<ea0c4380>] psr: 20000013 sp : ea48ff68 ip : 00000001 fp : 0000869c r10: 00000200 r9 : ea48e000 r8 : c020f4e4 r7 : 000000c5 r6 : ea48e000 r5 : ea48ffb0 r4 : ea490800 r3 : bef1e718 r2 : 00000001 r1 : 000000c5 r0 : 40000028 Flags: nzCv IRQs on FIQs on Mode SVC_32 ISA ARM Segment user Control: 10c5387d Table: 8a4ac059 DAC: 00000015 Process syscall_arm (pid: 61, stack limit = 0xea48e250) Stack: (0xea48ff68 to 0xea490000) ff60: 540e7a69 3ab5e840 00000200 000000c5 ea48ffb0 ea48e000 ff80: 000000c5 c02114bc bef1e718 00000001 b6efdb58 ffffffff 08400000 000000c5 ffa0: c020f4e4 c020f49c b6efdb58 ffffffff 00000001 bef1e718 bef1e718 00000001 ffc0: b6efdb58 ffffffff 08400000 000000c5 00000000 b6f22850 00000008 0000869c ffe0: 000000c5 bef1e704 b6ea315f b6e318e6 20000030 00000001 00000000 00000000 [<c02b2ae8>] (__audit_syscall_entry) from [<c02114bc>] (syscall_trace_enter+0xf0/0x120) [<c02114bc>] (syscall_trace_enter) from [<c020f49c>] (__sys_trace+0xc/0x38) Code: e584500c e5842004 e28dd00c e8bd80f0 (e7f001f2) ---[ end trace 0c4441660aba5692 ]--- In fact, syscall(-1) just fails (not signaled despite the expectation, this is another minor bug), but the succeeding syscall hits BUG_ON. When auditing syscall(-1), audit_syscall_entry() is called anyway, but audit_syscall_exit() is not called and then 'in_syscall' flag in thread's audit context is kept on. In this way, audit_syscall_entry() against the succeeding syscall will see BUG_ON(in_syscall). This patch fixes this bug by 1) preventing syscall tracing, ftrace tracepoint and audit, from being executed in case of invalid or pseudo system calls, 2) handling user-issued syscall(-1) with arm_syscall(). Signed-off-by: AKASHI Takahiro <takahiro.akashi@linaro.org> --- arch/arm/include/asm/traps.h | 1 + arch/arm/kernel/entry-common.S | 4 ++-- arch/arm/kernel/ptrace.c | 47 +++++++++++++++++++++++++--------------- 3 files changed, 32 insertions(+), 20 deletions(-)