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@citrix.com>
Signed-off-by: Jan Beulich <jbeulich@suse.com>
Acked-by: Andrew Cooper <andrew.cooper3@citrix.com>
Tested-by: Andrew Cooper <andrew.cooper3@citrix.com>
x86: comment update after "drop high compat r/o M2P table address range"

Commit 5af040ef8b57 clearly should also have updated the comment, not
just the #define-s.

Signed-off-by: Jan Beulich <jbeulich@suse.com>
Acked-by: Andrew Cooper <andrew.cooper3@citrix.com>
master commit: b6a907f8c83d37886d0523f1aeff61b98e133498
master date: 2020-07-31 17:41:58 +0200
master commit: 2e98d0b1d09e99e3d1287cb13f42b604ebc3c29a
master date: 2020-08-05 10:21:22 +0200

diff --git a/xen/arch/x86/x86_emulate/x86_emulate.c b/xen/arch/x86/x86_emulate/x86_emulate.c
index 84bb8e0c9bf2d00046d58ec28a00176655a64257..ee6341b1b769cd80e82ff522335af230438d1077 100644 (file)
--- a/xen/arch/x86/x86_emulate/x86_emulate.c
+++ b/xen/arch/x86/x86_emulate/x86_emulate.c
@@ -3368,7 +3368,7 @@ x86_decode(
         {
             generate_exception_if(d & vSIB, EXC_UD);
             modrm_rm |= ((rex_prefix & 1) << 3) |
-                        (evex_encoded() && !evex.x) << 4;
+                        ((evex_encoded() && !evex.x) << 4);
             ea.type = OP_REG;
         }
         else if ( ad_bytes == 2 )
@@ -3415,7 +3415,7 @@ 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);
@@ -3477,7 +3477,7 @@ 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);
@@ -9727,7 +9727,7 @@ 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 )
                 {
@@ -9849,7 +9849,8 @@ x86_emulate(
                 continue;
 
             rc = ops->read(ea.mem.seg,
-                           truncate_ea(ea.mem.off + (idx << state->sib_scale)),
+                           truncate_ea(ea.mem.off +
+                                       idx * (1 << state->sib_scale)),
                            (void *)mmvalp + i * op_bytes, op_bytes, ctxt);
             if ( rc != X86EMUL_OKAY )
             {
@@ -10020,7 +10021,8 @@ x86_emulate(
                 continue;
 
             rc = ops->write(ea.mem.seg,
-                            truncate_ea(ea.mem.off + (idx << state->sib_scale)),
+                            truncate_ea(ea.mem.off +
+                                        idx * (1 << state->sib_scale)),
                             (void *)mmvalp + i * op_bytes, op_bytes, ctxt);
             if ( rc != X86EMUL_OKAY )
             {
@@ -10138,7 +10140,7 @@ x86_emulate(
                   ? ops->write
                   : ops->read)(ea.mem.seg,
                                truncate_ea(ea.mem.off +
-                                           (idx << state->sib_scale)),
+                                           idx * (1 << state->sib_scale)),
                                NULL, 0, ctxt);
             if ( rc == X86EMUL_EXCEPTION )
             {