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