On Tue, Feb 23 2021 at 10:15, Andy Lutomirski wrote:

On a 32-bit fast syscall that fails to read its arguments from user memory, the kernel currently does syscall exit work but not syscall entry work. This confuses audit and ptrace. For example:

$ ./tools/testing/selftests/x86/syscall_arg_fault_32
...
strace: pid 264258: entering, ptrace_syscall_info.op == 2
...

This is a minimal fix intended for ease of backporting. A more complete cleanup is coming.

Cc: stable@vger.kernel.org Fixes: 0b085e68f407 ("x86/entry: Consolidate 32/64 bit syscall entry") Signed-off-by: Andy Lutomirski luto@kernel.org

---

arch/x86/entry/common.c | 3 ++- 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/arch/x86/entry/common.c b/arch/x86/entry/common.c index 0904f5676e4d..cf4dcf346ca8 100644 --- a/arch/x86/entry/common.c +++ b/arch/x86/entry/common.c @@ -128,7 +128,8 @@ static noinstr bool __do_fast_syscall_32(struct pt_regs *regs) regs->ax = -EFAULT; instrumentation_end();

• syscall_exit_to_user_mode(regs);
  

• local_irq_disable();
  

• exit_to_user_mode();
  

That's still the same as the previous version. The right function (while the name is misleading) to invoke here is irqentry_exit_to_user_mode() because that invokes exit_to_user_mode_prepare() before exit_to_user_mode(). We can rename that function afterwards.

Thanks,

tglx