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SubjectRe: CONFIG_PAGE_TABLE_ISOLATION=y on x86_64 causes gcc to segfault when building x86_32 binaries
On Wed, Jan 3, 2018 at 10:52 AM, Thomas Gleixner <tglx@linutronix.de> wrote:
> On Wed, 3 Jan 2018, Thomas Gleixner wrote:
>
>> On Wed, 3 Jan 2018, Lars Wendler wrote:
>> > Am Wed, 3 Jan 2018 13:05:38 +0100 (CET)
>> > schrieb Thomas Gleixner <tglx@linutronix.de>:
>> > > Also can you please try Linus v4.15-rc6 with PTI enabled so we can see
>> > > whether that's a backport issue or a general one?
>> >
>> > Same problem with 4.15-rc6. So I suppose that means it's a general
>> > issue.
>>
>> Just a shot in the dark as I just decoded another issue on a AMD CPU. Can
>> you please try the patch below?
>
> Ok. Found the real issue. This is a problem on AMD boxen.
>
> Fix below.
>
> Can Xen folks please have a look at that as well?
>
> Thanks,
>
> tglx
>
> 8<-------------------
>
> arch/x86/entry/entry_64_compat.S | 13 ++++++-------
> 1 file changed, 6 insertions(+), 7 deletions(-)
>
> --- a/arch/x86/entry/entry_64_compat.S
> +++ b/arch/x86/entry/entry_64_compat.S
> @@ -190,8 +190,13 @@ ENTRY(entry_SYSCALL_compat)
> /* Interrupts are off on entry. */
> swapgs
>
> - /* Stash user ESP and switch to the kernel stack. */
> + /* Stash user ESP */
> movl %esp, %r8d
> +
> + /* Use %rsp as scratch reg. User ESP is stashed in r8 */
> + SWITCH_TO_KERNEL_CR3 scratch_reg=%rsp
> +
> + /* Switch to the kernel stack */
> movq PER_CPU_VAR(cpu_current_top_of_stack), %rsp
>
> /* Construct struct pt_regs on stack */
> @@ -220,12 +225,6 @@ GLOBAL(entry_SYSCALL_compat_after_hwfram
> pushq $0 /* pt_regs->r15 = 0 */
>
> /*
> - * We just saved %rdi so it is safe to clobber. It is not
> - * preserved during the C calls inside TRACE_IRQS_OFF anyway.
> - */
> - SWITCH_TO_KERNEL_CR3 scratch_reg=%rdi
> -
> - /*
> * User mode is traced as though IRQs are on, and SYSENTER
> * turned them off.
> */

What's the issue that this is fixing?

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