Messages in this thread | | | Date | Thu, 1 Nov 2012 20:25:31 +0000 | From | Russell King - ARM Linux <> | Subject | Re: [PATCH 3/4] arch/arm: allow a scno of -1 to not cause a SIGILL |
| |
On Thu, Nov 01, 2012 at 12:46:38PM -0700, Kees Cook wrote: > From: Will Drewry <wad@chromium.org> > > On tracehook-friendly platforms, a system call number of -1 falls > through without running much code or taking much action. > > ARM is different. This adds a lightweight check to arm_syscall() > to make sure that ARM behaves the same way. > > Signed-off-by: Will Drewry <wad@chromium.org> > Signed-off-by: Kees Cook <keescook@chromium.org> > --- > arch/arm/kernel/traps.c | 4 ++++ > 1 file changed, 4 insertions(+) > > diff --git a/arch/arm/kernel/traps.c b/arch/arm/kernel/traps.c > index b0179b8..f303ea6 100644 > --- a/arch/arm/kernel/traps.c > +++ b/arch/arm/kernel/traps.c > @@ -540,6 +540,10 @@ asmlinkage int arm_syscall(int no, struct pt_regs *regs) > struct thread_info *thread = current_thread_info(); > siginfo_t info; > > + /* Emulate/fallthrough. */ > + if (no == -1) > + return regs->ARM_r0; > +
This won't work properly with OABI. The problem is that OABI has an offset on its syscall numbers which is removed/added at appropriate times, and this is one of the places where it's put back. So you end up with -1 XOR 0x900000 here, not -1.
It'd probably be better to do this check in the asm code here, which prevents that yuckyness from affecting this.
__sys_trace: mov r1, scno add r0, sp, #S_OFF bl syscall_trace_enter
adr lr, BSYM(__sys_trace_return) @ return address mov scno, r0 @ syscall number (possibly new) add r1, sp, #S_R0 + S_OFF @ pointer to regs cmp scno, #NR_syscalls @ check upper syscall limit ldmccia r1, {r0 - r6} @ have to reload r0 - r6 stmccia sp, {r4, r5} @ and update the stack args ldrcc pc, [tbl, scno, lsl #2] @ call sys_* routine + cmp scno, #-1 bne 2b + b ret_slow_syscall
| |