lkml.org 
[lkml]   [2017]   [Sep]   [13]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
/
Date
From
SubjectRe: [PATCH] x86/asm/64: do not clear high 32 bits of syscall number when CONFIG_X86_X32=y

On 09/13, Dmitry V. Levin wrote:
>
> Before this change, CONFIG_X86_X32=y fastpath behaviour was different
> from slowpath:

and even with this change they differ if CONFIG_X86_X32=n? do_syscall_64()
does "nr & __SYSCALL_MASK" unconditionally, this clears the upper bits, no?

And why __SYSCALL_MASK is not "unsigned long" ? IOW, why do we want to silently
ignore the upper bits in $rax ?

Or I am totally confused?

Oleg.

> $ gcc -xc -Wall -O2 - <<'EOF'
> #include <unistd.h>
> #include <asm/unistd.h>
> int main(void) {
> unsigned long nr = ~0xffffffffUL | __NR_exit;
> return !!syscall(nr, 42, 1, 2, 3, 4, 5);
> }
> EOF
> $ ./a.out; echo \$?=$?
> $?=42
> $ strace -enone ./a.out
> syscall_18446744069414584380(0x2a, 0x1, 0x2, 0x3, 0x4, 0x5) = -1 (errno 38)
> +++ exited with 1 +++
>
> This change syncs CONFIG_X86_X32=y fastpath behaviour with the case
> when CONFIG_X86_X32 is not enabled.
>
> Fixes: fca460f95e92 ("x32: Handle the x32 system call flag")
> Cc: stable@vger.kernel.org
> Signed-off-by: Dmitry V. Levin <ldv@altlinux.org>
> ---
> arch/x86/entry/entry_64.S | 8 +++-----
> 1 file changed, 3 insertions(+), 5 deletions(-)
>
> diff --git a/arch/x86/entry/entry_64.S b/arch/x86/entry/entry_64.S
> index 4916725..3bab6af 100644
> --- a/arch/x86/entry/entry_64.S
> +++ b/arch/x86/entry/entry_64.S
> @@ -185,12 +185,10 @@ entry_SYSCALL_64_fastpath:
> */
> TRACE_IRQS_ON
> ENABLE_INTERRUPTS(CLBR_NONE)
> -#if __SYSCALL_MASK == ~0
> - cmpq $__NR_syscall_max, %rax
> -#else
> - andl $__SYSCALL_MASK, %eax
> - cmpl $__NR_syscall_max, %eax
> +#if __SYSCALL_MASK != ~0
> + andq $__SYSCALL_MASK, %rax
> #endif
> + cmpq $__NR_syscall_max, %rax
> ja 1f /* return -ENOSYS (already in pt_regs->ax) */
> movq %r10, %rcx
>
> --
> ldv

\
 
 \ /
  Last update: 2017-09-13 18:49    [W:0.063 / U:1.372 seconds]
©2003-2017 Jasper Spaans. hosted at Digital OceanAdvertise on this site