Messages in this thread Patch in this message | | | From | Kees Cook <> | Subject | [PATCH] ARM: ptrace: Restore syscall skipping and restart while tracing | Date | Fri, 4 Aug 2023 00:10:53 -0700 |
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Since commit 4e57a4ddf6b0 ("ARM: 9107/1: syscall: always store thread_info->abi_syscall"), the seccomp selftests "syscall_errno", "syscall_faked", and "syscall_restart" have been broken. This was related to two issues:
- seccomp and PTRACE depend on using the special value of "-1" for skipping syscalls. This value wasn't working because it was getting masked by __NR_SYSCALL_MASK in both PTRACE_SET_SYSCALL and get_syscall_nr().
- the syscall entry label "local_restart" is used for resuming syscalls interrupted by signals, but the updated syscall number (in scno) was not being stored in current_thread_info()->abi_syscall, causing traced syscall restarting to fail.
Explicitly test for -1 in PTRACE_SET_SYSCALL and get_syscall_nr(), leaving it exposed when present, allowing tracers to skip syscalls again.
Move the AEABI-only assignment of current_thread_info()->abi_syscall after the "local_restart" label to allow tracers to survive syscall restarting.
Cc: Russell King <linux@armlinux.org.uk> Cc: Arnd Bergmann <arnd@kernel.org> Cc: Lecopzer Chen <lecopzer.chen@mediatek.com> Cc: Oleg Nesterov <oleg@redhat.com> Cc: linux-arm-kernel@lists.infradead.org Fixes: 4e57a4ddf6b0 ("ARM: 9107/1: syscall: always store thread_info->abi_syscall") Signed-off-by: Kees Cook <keescook@chromium.org> --- Note that I haven't tested OABI at all, and AEABI+OABI_COMPAT doesn't work with seccomp. I booted an AEABI system under AEABI+OABI_COMPAT, but I wasn't able to test tracing... --- arch/arm/include/asm/syscall.h | 3 +++ arch/arm/kernel/entry-common.S | 5 +++-- arch/arm/kernel/ptrace.c | 5 +++-- 3 files changed, 9 insertions(+), 4 deletions(-)
diff --git a/arch/arm/include/asm/syscall.h b/arch/arm/include/asm/syscall.h index dfeed440254a..fe4326d938c1 100644 --- a/arch/arm/include/asm/syscall.h +++ b/arch/arm/include/asm/syscall.h @@ -25,6 +25,9 @@ static inline int syscall_get_nr(struct task_struct *task, if (IS_ENABLED(CONFIG_AEABI) && !IS_ENABLED(CONFIG_OABI_COMPAT)) return task_thread_info(task)->abi_syscall; + if (task_thread_info(task)->abi_syscall == -1) + return -1; + return task_thread_info(task)->abi_syscall & __NR_SYSCALL_MASK; } diff --git a/arch/arm/kernel/entry-common.S b/arch/arm/kernel/entry-common.S index bcc4c9ec3aa4..08bd624e4c6f 100644 --- a/arch/arm/kernel/entry-common.S +++ b/arch/arm/kernel/entry-common.S @@ -246,8 +246,6 @@ ENTRY(vector_swi) bic scno, scno, #0xff000000 @ mask off SWI op-code str scno, [tsk, #TI_ABI_SYSCALL] eor scno, scno, #__NR_SYSCALL_BASE @ check OS number -#else - str scno, [tsk, #TI_ABI_SYSCALL] #endif /* * Reload the registers that may have been corrupted on entry to @@ -256,6 +254,9 @@ ENTRY(vector_swi) TRACE( ldmia sp, {r0 - r3} ) local_restart: +#if defined(CONFIG_AEABI) && !defined(CONFIG_OABI_COMPAT) + str scno, [tsk, #TI_ABI_SYSCALL] @ store scno for syscall restart +#endif ldr r10, [tsk, #TI_FLAGS] @ check for syscall tracing stmdb sp!, {r4, r5} @ push fifth and sixth args diff --git a/arch/arm/kernel/ptrace.c b/arch/arm/kernel/ptrace.c index 2d8e2516906b..fef32d73f912 100644 --- a/arch/arm/kernel/ptrace.c +++ b/arch/arm/kernel/ptrace.c @@ -783,8 +783,9 @@ long arch_ptrace(struct task_struct *child, long request, break; case PTRACE_SET_SYSCALL: - task_thread_info(child)->abi_syscall = data & - __NR_SYSCALL_MASK; + if (data != -1) + data &= __NR_SYSCALL_MASK; + task_thread_info(child)->abi_syscall = data; ret = 0; break; -- 2.34.1
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