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SubjectRe: [RFC PATCH v2 18/27] x86/cet/shstk: Introduce WRUSS instruction
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> +/*
> + * WRUSS is a kernel instrcution and but writes to user
> + * shadow stack memory. When a fault occurs, both
> + * X86_PF_USER and X86_PF_SHSTK are set.
> + */
> +static int is_wruss(struct pt_regs *regs, unsigned long error_code)
> +{
> + return (((error_code & (X86_PF_USER | X86_PF_SHSTK)) ==
> + (X86_PF_USER | X86_PF_SHSTK)) && !user_mode(regs));
> +}

I thought X86_PF_USER was set based on the mode in which the fault
occurred. Does this mean that the architecture of this bit is different
now?

That seems like something we need to call out if so. It also means we
need to update the SDM because some of the text is wrong.

> static void
> show_fault_oops(struct pt_regs *regs, unsigned long error_code,
> unsigned long address)
> @@ -848,7 +859,7 @@ __bad_area_nosemaphore(struct pt_regs *regs, unsigned long error_code,
> struct task_struct *tsk = current;
>
> /* User mode accesses just cause a SIGSEGV */
> - if (error_code & X86_PF_USER) {
> + if ((error_code & X86_PF_USER) && !is_wruss(regs, error_code)) {
> /*
> * It's possible to have interrupts off here:
> */

This needs commenting about why is_wruss() is special.

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