6.4-stable review patch. If anyone has any objections, please let me know.
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From: Kees Cook keescook@chromium.org
[ Upstream commit 4697b5848bd933f68ebd04836362c8de0cacaf71 ]
Since commit 4e57a4ddf6b0 ("ARM: 9107/1: syscall: always store thread_info->abi_syscall"), the seccomp selftests "syscall_errno" and "syscall_faked" have been broken. Both 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().
Explicitly test for -1 in PTRACE_SET_SYSCALL and get_syscall_nr(), leaving it exposed when present, allowing tracers to skip syscalls again.
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") Reviewed-by: Arnd Bergmann arnd@arndb.de Link: https://lore.kernel.org/r/20230810195422.2304827-2-keescook@chromium.org Signed-off-by: Kees Cook keescook@chromium.org Signed-off-by: Sasha Levin sashal@kernel.org --- arch/arm/include/asm/syscall.h | 3 +++ arch/arm/kernel/ptrace.c | 5 +++-- 2 files changed, 6 insertions(+), 2 deletions(-)
diff --git a/arch/arm/include/asm/syscall.h b/arch/arm/include/asm/syscall.h index dfeed440254a8..fe4326d938c18 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/ptrace.c b/arch/arm/kernel/ptrace.c index 2d8e2516906b6..fef32d73f9120 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;