Andi Kleen wrote:
> From: Jeff Dike <[email protected]>
> The patch below copies %r9 (where the sixth argument has been
> stashed) into the RBP slot of pt_regs before syscall_trace_enter is
> called. This fixes ptrace.
>
> To allow a successful return to userspace, the original value of rbp
> must be restored. This is done by storing the current value of rbp
> into the RBP slot of pt_regs before the RESTORE_REST.
>
> --- linux.orig/arch/x86_64/ia32/ia32entry.S
> +++ linux/arch/x86_64/ia32/ia32entry.S
> @@ -148,11 +148,23 @@ sysenter_do_call:
> sysenter_tracesys:
> CFI_RESTORE_STATE
> SAVE_REST
> + /*
> + * We need the 6th system call argument to be in regs->rbp at
> + * this point so that ptrace will see it. It's in r9 now, so copy
> + * it to the rbp slot now.
> + */
> + movq %r9, RBP(%rsp)
> CLEAR_RREGS
> movq $-ENOSYS,RAX(%rsp) /* really needed? */
> movq %rsp,%rdi /* &pt_regs -> arg1 */
> call syscall_trace_enter
> LOAD_ARGS ARGOFFSET /* reload args from stack in case ptrace changed it */
> + /*
> + * Now, we need the correct value of rbp to be restored. It
> + * was never munged, so we can save it to the rbp slot and
> + * just have it restored.
> + */
> + movq %rbp, RBP(%rsp)
> RESTORE_REST
> movl %ebp, %ebp
> /* no need to do an access_ok check here because rbp has been
Didn't we have problems with this exact approach before? This one was dropped
because it caused 32-bit programs to crash:
http://www2.kernel.org/pub/linux/kernel/people/akpm/patches/2.6/2.6.13/2.6.13-mm2/broken-out/x86-64-ptrace-ia32-bp-fix.patch
See:
http://lkml.org/lkml/2005/09/16/261
for the one I proposed instead.
And in any case doesn't cstar_tracesys() need the same fix?
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