[PATCH 6.5 021/739] ARM: ptrace: Restore syscall restart tracing

[PATCH 6.5 021/739] ARM: ptrace: Restore syscall restart tracing

[Greg Kroah-Hartman]

6.5-stable review patch.  If anyone has any objections, please let me know.

------------------

From: Kees Cook <keescook@chromium.org>

[ Upstream commit cf007647475b5090819c5fe8da771073145c7334 ]

Since commit 4e57a4ddf6b0 ("ARM: 9107/1: syscall: always store
thread_info->abi_syscall"), the seccomp selftests "syscall_restart" has
been broken. This was caused by the restart syscall not being stored to
"abi_syscall" during restart setup before branching to the "local_restart"
label. Tracers would see the wrong syscall, and scno would get overwritten
while returning from the TIF_WORK path. Add the missing store.

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/20230810195422.2304827-1-keescook@chromium.org
Signed-off-by: Kees Cook <keescook@chromium.org>
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
 arch/arm/kernel/entry-common.S | 1 +
 1 file changed, 1 insertion(+)

diff --git a/arch/arm/kernel/entry-common.S b/arch/arm/kernel/entry-common.S
index bcc4c9ec3aa4e..5c31e9de7a602 100644
--- a/arch/arm/kernel/entry-common.S
+++ b/arch/arm/kernel/entry-common.S
@@ -90,6 +90,7 @@ slow_work_pending:
 	cmp	r0, #0
 	beq	no_work_pending
 	movlt	scno, #(__NR_restart_syscall - __NR_SYSCALL_BASE)
+	str	scno, [tsk, #TI_ABI_SYSCALL]	@ make sure tracers see update
 	ldmia	sp, {r0 - r6}			@ have to reload r0 - r6
 	b	local_restart			@ ... and off we go
 ENDPROC(ret_fast_syscall)
-- 
2.40.1




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[PATCH 6.5 022/739] ARM: ptrace: Restore syscall skipping for tracers

[Greg Kroah-Hartman]

6.5-stable review patch.  If anyone has any objections, please let me know.

------------------

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;
 
-- 
2.40.1




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