Re: [PATCH 1/2] x86/uprobes: Keep shadow stack in sync for emulated CALLs
From: Peter Zijlstra <peterz@infradead.org>
Date: 2026-06-23 08:43:36
Also in:
linux-kselftest, lkml
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")
?
quoted hunk ↗ jump to hunk
Signed-off-by: David Windsor <redacted> --- 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