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sh: fix syscall tracing

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Addition of SECCOMP_FILTER exposed a longstanding bug in
do_syscall_trace_enter, whereby r0 (the 5th argument register) was
mistakenly used where r3 (syscall_nr) was intended. By overwriting r0
rather than r3 with -1 when attempting to block a syscall, the
existing code would instead have caused the syscall to execute with an
argument clobbered.

Commit 0bb605c2c7 then introduced skipping of the syscall when
do_syscall_trace_enter returns -1, so that the return value set by
seccomp filters would not be clobbered by -ENOSYS. This eliminated the
clobbering of the 5th argument register, but instead caused syscalls
made with a 5th argument of -1 to be misinterpreted as a request by
do_syscall_trace_enter to suppress the syscall.

Fixes: 0bb605c2c7 ("sh: Add SECCOMP_FILTER")
Fixes: ab99c733ae ("sh: Make syscall tracer use tracehook notifiers, add TIF_NOTIFY_RESUME.")
Tested-by: John Paul Adrian Glaubitz <glaubitz@physik.fu-berlin.de>
Signed-off-by: Rich Felker <dalias@libc.org>
This commit is contained in:
Rich Felker 2020-08-28 21:01:41 -04:00
parent ca6345de57
commit b0cfc315ff
2 changed files with 5 additions and 11 deletions
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1
arch/sh/kernel/entry-common.S
View File

@ -370,7 +370,6 @@ syscall_trace_entry:
nop
cmp/eq #-1, r0
bt syscall_exit
mov.l r0, @(OFF_R0,r15) ! Save return value
! Reload R0-R4 from kernel stack, where the
! parent may have modified them using
! ptrace(POKEUSR). (Note that R0-R2 are

15
arch/sh/kernel/ptrace_32.c
View File

@ -455,16 +455,11 @@ long arch_ptrace(struct task_struct *child, long request,
asmlinkage long do_syscall_trace_enter(struct pt_regs *regs)
{
long ret = 0;
if (test_thread_flag(TIF_SYSCALL_TRACE) &&
tracehook_report_syscall_entry(regs))
/*
* Tracing decided this syscall should not happen.
* We'll return a bogus call number to get an ENOSYS
* error, but leave the original number in regs->regs[0].
*/
ret = -1L;
tracehook_report_syscall_entry(regs)) {
regs->regs[0] = -ENOSYS;
return -1;
}
if (secure_computing() == -1)
return -1;
@ -475,7 +470,7 @@ asmlinkage long do_syscall_trace_enter(struct pt_regs *regs)
audit_syscall_entry(regs->regs[3], regs->regs[4], regs->regs[5],
regs->regs[6], regs->regs[7]);
return ret ?: regs->regs[0];
return 0;
}
asmlinkage void do_syscall_trace_leave(struct pt_regs *regs)