[xen staging-4.21] x86/pv32: Fix bogus CR2 in pagefault for gate emulation

[patchbot@xxxxxxx]

commit 647e362ad170708e6d7b53d0725cd3e30fb94d84
Author:     Teddy Astie <teddy.astie@xxxxxxxxxx>
AuthorDate: Wed Jun 3 11:37:32 2026 +0200
Commit:     Jan Beulich <jbeulich@xxxxxxxx>
CommitDate: Wed Jun 3 11:37:32 2026 +0200

    x86/pv32: Fix bogus CR2 in pagefault for gate emulation
    
    __{put,get}_guest() returns -EFAULT on access faults which causes
    the injected CR2 to be off by 14 bytes (as EFAULT is 14) which is
    incorrect.
    
    Fix the computation by relying on __copy_{from,to}_guest_pv() which
    reports the number of remaining bytes instead of a negative errno,
    such that we can compute the offset properly.
    
    Fixes: 70ad570b2799 ("x86/64: paravirt 32-on-64 call gate support")
    Signed-off-by: Teddy Astie <teddy.astie@xxxxxxxxxx>
    Reviewed-by: Jan Beulich <jbeulich@xxxxxxxx>
    master commit: 03878fba4af14fab942c2ce8ed2d6d18c204a603
    master date: 2026-05-22 14:33:44 +0100
---
 xen/arch/x86/pv/emul-gate-op.c | 6 ++++--
 1 file changed, 4 insertions(+), 2 deletions(-)

diff --git a/xen/arch/x86/pv/emul-gate-op.c b/xen/arch/x86/pv/emul-gate-op.c
index dcac0a0401..1fcab1f3a3 100644
--- a/xen/arch/x86/pv/emul-gate-op.c
+++ b/xen/arch/x86/pv/emul-gate-op.c
@@ -284,12 +284,14 @@ void pv_emulate_gate_op(struct cpu_user_regs *regs)
     if ( !jump )
     {
         unsigned int ss, esp, *stkp;
+        uint32_t value;
         int rc;
 #define push(item) do \
         { \
+            value = (item); \
             --stkp; \
             esp -= 4; \
-            rc = __put_guest(item, stkp); \
+            rc = __copy_to_guest_pv(stkp, &value, sizeof(value)); \
             if ( rc ) \
             { \
                 pv_inject_page_fault(PFEC_write_access, \
@@ -357,7 +359,7 @@ void pv_emulate_gate_op(struct cpu_user_regs *regs)
                     unsigned int parm;
 
                     --ustkp;
-                    rc = __get_guest(parm, ustkp);
+                    rc = __copy_from_guest_pv(&parm, ustkp, sizeof(parm));
                     if ( rc )
                     {
                         pv_inject_page_fault(0, (unsigned long)(ustkp + 1) - 
rc);
--
generated by git-patchbot for /home/xen/git/xen.git#staging-4.21