Re: [PATCH v2 3/5] x86/mce: add EX_TYPE_EFAULT_REG as in-kernel recovery context to fix copy-from-user operations regression
From: Peter Zijlstra
Date: Tue Feb 18 2025 - 08:06:14 EST
On Tue, Feb 18, 2025 at 01:54:08PM +0100, Peter Zijlstra wrote:
> ---
> diff --git a/arch/x86/kernel/cpu/mce/severity.c b/arch/x86/kernel/cpu/mce/severity.c
> index dac4d64dfb2a..cb021058165f 100644
> --- a/arch/x86/kernel/cpu/mce/severity.c
> +++ b/arch/x86/kernel/cpu/mce/severity.c
> @@ -300,13 +300,12 @@ static noinstr int error_context(struct mce *m, struct pt_regs *regs)
> copy_user = is_copy_from_user(regs);
> instrumentation_end();
>
> - switch (fixup_type) {
> - case EX_TYPE_UACCESS:
> - if (!copy_user)
> - return IN_KERNEL;
> - m->kflags |= MCE_IN_KERNEL_COPYIN;
> - fallthrough;
> + if (copy_user) {
> + m->kflags |= MCE_IN_KERNEL_COPYIN | MCE_IN_KERNEL_COPYIN;
Typing is hard, obviously that second should'be been _RECOV.
> + return IN_KERNEL_RECOV
But why are we having that bit *and* a return value saying the same
thing?
> + }
>
> + switch (fixup_type) {
> case EX_TYPE_FAULT_MCE_SAFE:
> case EX_TYPE_DEFAULT_MCE_SAFE:
> m->kflags |= MCE_IN_KERNEL_RECOV;