[xen stable-4.12] x86emul: replace UB shifts

[patchbot@xxxxxxx]

commit dca9cc7db628040a8b673a3e5cf7df237429bd68
Author:     Jan Beulich <jbeulich@xxxxxxxx>
AuthorDate: Fri Aug 7 17:32:42 2020 +0200
Commit:     Jan Beulich <jbeulich@xxxxxxxx>
CommitDate: Fri Aug 7 17:32:42 2020 +0200

    x86emul: replace UB shifts
    
    Displacement values can be negative, hence we shouldn't left-shift them.
    Or else we get
    
    (XEN) UBSAN: Undefined behaviour in x86_emulate/x86_emulate.c:3482:55
    (XEN) left shift of negative value -2
    
    While auditing shifts, I noticed a pair of missing parentheses, which
    also get added right here.
    
    Reported-by: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
    Signed-off-by: Jan Beulich <jbeulich@xxxxxxxx>
    Acked-by: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
    Tested-by: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
    
    x86emul: replace further UB shifts
    
    I have no explanation how I managed to overlook these while putting
    together what is now b6a907f8c83d ("x86emul: replace UB shifts").
    
    Signed-off-by: Jan Beulich <jbeulich@xxxxxxxx>
    Acked-by: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
    master commit: b6a907f8c83d37886d0523f1aeff61b98e133498
    master date: 2020-07-31 17:41:58 +0200
    master commit: 21de9680eb594a7038d4d4ed78e53ac90a8c5a6e
    master date: 2020-08-05 10:19:29 +0200
---
 xen/arch/x86/x86_emulate/x86_emulate.c | 6 +++---
 1 file changed, 3 insertions(+), 3 deletions(-)

diff --git a/xen/arch/x86/x86_emulate/x86_emulate.c 
b/xen/arch/x86/x86_emulate/x86_emulate.c
index 98f52083f8..09de6ee15d 100644
--- a/xen/arch/x86/x86_emulate/x86_emulate.c
+++ b/xen/arch/x86/x86_emulate/x86_emulate.c
@@ -3131,7 +3131,7 @@ x86_decode(
                     ea.mem.off = insn_fetch_type(int16_t);
                 break;
             case 1:
-                ea.mem.off += insn_fetch_type(int8_t) << disp8scale;
+                ea.mem.off += insn_fetch_type(int8_t) * (1 << disp8scale);
                 break;
             case 2:
                 ea.mem.off += insn_fetch_type(int16_t);
@@ -3190,7 +3190,7 @@ x86_decode(
                 pc_rel = mode_64bit();
                 break;
             case 1:
-                ea.mem.off += insn_fetch_type(int8_t) << disp8scale;
+                ea.mem.off += insn_fetch_type(int8_t) * (1 << disp8scale);
                 break;
             case 2:
                 ea.mem.off += insn_fetch_type(int32_t);
@@ -8521,7 +8521,7 @@ x86_emulate(
 
                 rc = ops->read(ea.mem.seg,
                                truncate_ea(ea.mem.off +
-                                           (idx << state->sib_scale)),
+                                           idx * (1 << state->sib_scale)),
                                (void *)mmvalp + i * op_bytes, op_bytes, ctxt);
                 if ( rc != X86EMUL_OKAY )
                 {
--
generated by git-patchbot for /home/xen/git/xen.git#stable-4.12