Re: [PATCH 1/2] x86/uprobes: Keep shadow stack in sync for emulated CALLs

[Peter Zijlstra]

On Mon, Jun 22, 2026 at 02:31:08PM -0400, David Windsor wrote:
> Uprobe CALL emulation updates the normal user stack, but not the CET user
> shadow stack. The subsequent RET then sees a stale shadow stack entry and
> raises #CP.
> 
> Update the relative CALL emulation and XOL CALL fixup paths to keep the
> shadow stack in sync.
> 
> Fixes: 488af8ea7131 ("x86/shstk: Wire in shadow stack interface")

I can confirm this patch fixes the included test case, so yay for that.

However, should this not be:

Fixes: 1713b63a07a2 ("x86/shstk: Make return uprobe work with shadow stack")

?

> Signed-off-by: David Windsor <dwindsor@xxxxxxxxx>
> ---
>  arch/x86/kernel/uprobes.c | 10 +++++++++-
>  1 file changed, 9 insertions(+), 1 deletion(-)
> 
> diff --git a/arch/x86/kernel/uprobes.c b/arch/x86/kernel/uprobes.c
> index ebb1baf1eb1d..ae32013a7097 100644
> --- a/arch/x86/kernel/uprobes.c
> +++ b/arch/x86/kernel/uprobes.c
> @@ -1246,8 +1246,12 @@ static int default_post_xol_op(struct arch_uprobe *auprobe, struct pt_regs *regs
>  		long correction = utask->vaddr - utask->xol_vaddr;
>  		regs->ip += correction;
>  	} else if (auprobe->defparam.fixups & UPROBE_FIX_CALL) {
> +		unsigned long retaddr = utask->vaddr + auprobe->defparam.ilen;
> +
>  		regs->sp += sizeof_long(regs); /* Pop incorrect return address */
> -		if (emulate_push_stack(regs, utask->vaddr + auprobe->defparam.ilen))
> +		if (emulate_push_stack(regs, retaddr))
> +			return -ERESTART;
> +		if (shstk_update_last_frame(retaddr))
>  			return -ERESTART;
>  	}
>  	/* popf; tell the caller to not touch TF */
> @@ -1338,6 +1342,10 @@ static bool branch_emulate_op(struct arch_uprobe *auprobe, struct pt_regs *regs)
>  		 */
>  		if (emulate_push_stack(regs, new_ip))
>  			return false;
> +		if (shstk_push(new_ip) == -EFAULT) {
> +			regs->sp += sizeof_long(regs);
> +			return false;
> +		}
>  	} else if (!check_jmp_cond(auprobe, regs)) {
>  		offs = 0;
>  	}
> -- 
> 2.43.0