Re: [PATCH] pv32: Fix bogus cr2 on fault in emulation gate

[Andrew Cooper <andrew.cooper3@xxxxxxxxxx>]

On 20/05/2026 4:51 pm, Teddy Astie wrote:
> __{put,get}_guest returns -EFAULT on access faults which causes
> the injected cr2 to be off by 14 bytes (as EFAULT is 14) which is
> incorrect.
>
> Fix the computation by relying on copy_{from,to}_guest_pv which
> reports the number of remaining bytes instead of a negative errno,
> such that we can compute the offset properly.
>
> Fixes: 70ad570b2799 ("x86/64: paravirt 32-on-64 call gate support")
> Signed-off-by: Teddy Astie <teddy.astie@xxxxxxxxxx>
> ---
>  xen/arch/x86/pv/emul-gate-op.c | 5 +++--
>  1 file changed, 3 insertions(+), 2 deletions(-)
>
> diff --git a/xen/arch/x86/pv/emul-gate-op.c b/xen/arch/x86/pv/emul-gate-op.c
> index c2c699fbff..cacc171115 100644
> --- a/xen/arch/x86/pv/emul-gate-op.c
> +++ b/xen/arch/x86/pv/emul-gate-op.c
> @@ -289,9 +289,10 @@ void pv_emulate_gate_op(struct cpu_user_regs *regs)
>          int rc;
>  #define push(item) do \
>          { \
> +            unsigned int __value = item; \
>              --stkp; \
>              esp -= 4; \
> -            rc = __put_guest(item, stkp); \
> +            rc = copy_to_guest_pv(stkp, &__value, sizeof(__value)); \

Oh, this probably violates MISRA, but you don't need to use a separate
variable because sizeof() has no side effects.

Given that the expression is now &item, I think it needs to be &(item).

Can also be fixed on commit.

~Andrew