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SubjectRe: [PATCH] sh: fix syscall tracing
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Hi Rich!

On 9/3/20 7:48 AM, Rich Felker wrote:
> 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 0bb605c2c7f2b4b3 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: 0bb605c2c7f2b4b3 ("sh: Add SECCOMP_FILTER")
> Fixes: ab99c733ae73cce3 ("sh: Make syscall tracer use tracehook notifiers, add TIF_NOTIFY_RESUME.")
> Signed-off-by: Rich Felker <dalias@libc.org>
> ---
> arch/sh/kernel/entry-common.S | 1 -
> arch/sh/kernel/ptrace_32.c | 15 +++++----------
> 2 files changed, 5 insertions(+), 11 deletions(-)
>
> diff --git a/arch/sh/kernel/entry-common.S b/arch/sh/kernel/entry-common.S
> index ad963104d22d..91ab2607a1ff 100644
> --- a/arch/sh/kernel/entry-common.S
> +++ b/arch/sh/kernel/entry-common.S
> @@ -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
> diff --git a/arch/sh/kernel/ptrace_32.c b/arch/sh/kernel/ptrace_32.c
> index b05bf92f9c32..5281685f6ad1 100644
> --- a/arch/sh/kernel/ptrace_32.c
> +++ b/arch/sh/kernel/ptrace_32.c
> @@ -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)
>

I can confirm that this patch fixes both strace for me and does not break libseccomp,
I have run the libseccomp testsuite with my patch for SuperH support applied on top
of a rebased libseccomp with the 32-bit fixes. Attaching the testsuite log.

Tested-by: John Paul Adrian Glaubitz <glaubitz@physik.fu-berlin.de>

--
.''`. John Paul Adrian Glaubitz
: :' : Debian Developer - glaubitz@debian.org
`. `' Freie Universitaet Berlin - glaubitz@physik.fu-berlin.de
`- GPG: 62FF 8A75 84E0 2956 9546 0006 7426 3B37 F5B5 F913
=============== Thu 03 Sep 2020 11:57:57 AM CEST ===============
Regression Test Report ("regression -T live")
batch name: 01-sim-allow
test mode: c
test type: bpf-sim
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batch name: 05-sim-long_jumps
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batch name: 11-basic-basic_errors
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batch name: 12-sim-basic_masked_ops
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batch name: 13-basic-attrs
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batch name: 15-basic-resolver
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batch name: 16-sim-arch_basic
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batch name: 17-sim-arch_merge
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batch name: 19-sim-missing_syscalls
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batch name: 20-live-basic_die
test mode: c
test type: live
Test 20-live-basic_die%%001-00001 result: SUCCESS
Test 20-live-basic_die%%002-00001 result: SUCCESS
Test 20-live-basic_die%%003-00001 result: SUCCESS
batch name: 21-live-basic_allow
test mode: c
test type: live
Test 21-live-basic_allow%%001-00001 result: SUCCESS
batch name: 22-sim-basic_chains_array
test mode: c
test type: bpf-sim
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batch name: 23-sim-arch_all_le_basic
test mode: c
test type: bpf-sim
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batch name: 24-live-arg_allow
test mode: c
test type: live
Test 24-live-arg_allow%%001-00001 result: SUCCESS
batch name: 25-sim-multilevel_chains_adv
test mode: c
test type: bpf-sim
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batch name: 26-sim-arch_all_be_basic
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batch name: 32-live-tsync_allow
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Test 32-live-tsync_allow%%001-00001 result: SUCCESS
batch name: 33-sim-socket_syscalls_be
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batch name: 38-basic-pfc_coverage
test mode: c
test type: basic
batch name: 39-basic-api_level
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batch name: 40-sim-log
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batch name: 41-sim-syscall_priority_arch
test mode: c
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Test 44-live-a2_order%%001-00001 result: SUCCESS
batch name: 45-sim-chain_code_coverage
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Test 47-live-kill_process%%001-00001 result: SUCCESS
batch name: 48-sim-32b_args
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Test 51-live-user_notification%%001-00001 result: SUCCESS
batch name: 52-basic-load
test mode: c
test type: basic
batch name: 53-sim-binary_tree
test mode: c
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batch name: 54-live-binary_tree
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Test 54-live-binary_tree%%001-00001 result: SUCCESS
batch name: 55-basic-pfc_binary_tree
test mode: c
test type: basic
batch name: 56-basic-iterate_syscalls
test mode: c
test type: basic
batch name: 57-basic-rawsysrc
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test type: basic
batch name: 58-live-tsync_notify
test mode: c
test type: live
Test 58-live-tsync_notify%%001-00001 result: SUCCESS
Regression Test Summary
tests run: 11
tests skipped: 0
tests passed: 11
tests failed: 0
tests errored: 0
============================================================
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