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

[David Windsor]

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")
Signed-off-by: David Windsor <dwind...@gmail.com>
---
 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