* Roland McGrath <[EMAIL PROTECTED]> wrote:
> This makes the x86-64 behavior for 32-bit processes that set bogus
> %cs/%ss values (the only ones that can fault in iret) match what the
> native i386 behavior has been since:
>
> commit a879cbbb34cbecfa9707fbb6e5a00c503ac1ecb9
> Author: Linus Torvalds <[EMAIL PROTECTED]>
> Date: Fri Apr 29 09:38:44 2005 -0700
>
> x86: make traps on 'iret' be debuggable in user space
>
> Signed-off-by: Roland McGrath <[EMAIL PROTECTED]>
> ---
> arch/x86/kernel/entry_64.S | 25 +++++++++++++++++++------
> 1 files changed, 19 insertions(+), 6 deletions(-)
>
> diff --git a/arch/x86/kernel/entry_64.S b/arch/x86/kernel/entry_64.S
> index 07d4aba..62744b1 100644
> --- a/arch/x86/kernel/entry_64.S
> +++ b/arch/x86/kernel/entry_64.S
> @@ -592,13 +592,26 @@ ENTRY(native_iret)
> .quad native_iret, bad_iret
> .previous
> .section .fixup,"ax"
> - /* force a signal here? this matches i386 behaviour */
> - /* running with kernel gs */
> bad_iret:
> - movq $11,%rdi /* SIGSEGV */
> - TRACE_IRQS_ON
> - ENABLE_INTERRUPTS(CLBR_ANY | ~(CLBR_RDI))
> - jmp do_exit
> + /*
> + * The iret traps when the %cs or %ss being restored is bogus.
> + * (This can only happen in a 32-bit process, and only by invalid
> + * selectors being set via ptrace. Changing the value enforces
> + * that the USER_RPL bits are set, but not that the index is valid.)
> + * We've lost the original trap vector and error code.
> + * #GPF is the most likely one to get for an invalid selector.
> + * So pretend we completed the iret and took the #GPF in user mode.
> + *
> + * We are now running with the kernel GS after exception recovery.
> + * But error_entry expects us to have user GS to match the user %cs,
> + * so swap back.
> + */
> + INTR_FRAME
> + pushq $0
> + CFI_ADJUST_CFA_OFFSET 8
> + SWAPGS
> + jmp general_protection
> + CFI_ENDPROC
> .previous
thanks, applied. I suppose you have a testcase for this that we could
try?
Ingo
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