On Tue, Aug 16, 2022 at 09:11:37AM +0200, Juergen Gross wrote:
> Commit c89191ce67ef ("x86/entry: Convert SWAPGS to swapgs and remove
> the definition of SWAPGS") missed one use case of SWAPGS in
> entry_INT80_compat. Removing of the SWAPGS macro led to asm just
> using "swapgs", as it is accepting instructions in capital letters,
> too.
>
> This in turn leads to splats in Xen PV guests like:
>
> [ 36.145223] general protection fault, maybe for address 0x2d: 0000 [#1] PREEMPT SMP NOPTI
> [ 36.145794] CPU: 2 PID: 1847 Comm: ld-linux.so.2 Not tainted 5.19.1-1-default #1 openSUSE Tumbleweed f3b44bfb672cdb9f235aff53b57724eba8b9411b
> [ 36.146608] Hardware name: HP ProLiant ML350p Gen8, BIOS P72 11/14/2013
> [ 36.148126] RIP: e030:entry_INT80_compat+0x3/0xa3
>
> Fix that by open coding this single instance of the SWAPGS macro.
>
> Cc: <stable@xxxxxxxxxxxxxxx> # 5.19
> Fixes: c89191ce67ef ("x86/entry: Convert SWAPGS to swapgs and remove the definition of SWAPGS")
> Signed-off-by: Juergen Gross <jgross@xxxxxxxx>
It's a little unfortunate int80 is different from the other compat entry
points, but that's life I suppose.
Acked-by: Peter Zijlstra (Intel) <peterz@xxxxxxxxxxxxx>
> ---
> arch/x86/entry/entry_64_compat.S | 2 +-
> 1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/arch/x86/entry/entry_64_compat.S b/arch/x86/entry/entry_64_compat.S
> index 682338e7e2a3..4dd19819053a 100644
> --- a/arch/x86/entry/entry_64_compat.S
> +++ b/arch/x86/entry/entry_64_compat.S
> @@ -311,7 +311,7 @@ SYM_CODE_START(entry_INT80_compat)
> * Interrupts are off on entry.
> */
> ASM_CLAC /* Do this early to minimize exposure */
> - SWAPGS
> + ALTERNATIVE "swapgs", "", X86_FEATURE_XENPV
>
> /*
> * User tracing code (ptrace or signal handlers) might assume that
> --
> 2.35.3
>
