[Xen-changelog] [xen staging] libxc/x86: correct overflow avoidance check in AMD CPUID handling

[patchbot@xxxxxxx]

commit c9c7ac508b3f65f7d5f9685893096a1b22d8b176
Author:     Jan Beulich <jbeulich@xxxxxxxx>
AuthorDate: Wed Sep 25 15:50:58 2019 +0200
Commit:     Jan Beulich <jbeulich@xxxxxxxx>
CommitDate: Wed Sep 25 15:50:58 2019 +0200

    libxc/x86: correct overflow avoidance check in AMD CPUID handling
    
    Commit df29d03f1d ("libxc/x86: avoid certain overflows in CPUID APIC ID
    adjustments" introduced a one bit too narrow mask when checking whether
    multiplying by 1 (in particular in leaf 1) would result in overflow.
    
    Reported-by: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
    Signed-off-by: Jan Beulich <jbeulich@xxxxxxxx>
    Reviewed-by: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
---
 tools/libxc/xc_cpuid_x86.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/tools/libxc/xc_cpuid_x86.c b/tools/libxc/xc_cpuid_x86.c
index b472fbc610..54b0161132 100644
--- a/tools/libxc/xc_cpuid_x86.c
+++ b/tools/libxc/xc_cpuid_x86.c
@@ -403,7 +403,7 @@ static void amd_xc_cpuid_policy(const struct 
cpuid_domain_info *info,
          * - incrementing ApicIdCoreSize when it's zero (which changes the
          *   meaning of bits 7:0).
          */
-        if ( (regs[2] & 0x7fu) < 0x7fu )
+        if ( (regs[2] & 0xffu) < 0x7fu )
         {
             if ( (regs[2] & 0xf000u) && (regs[2] & 0xf000u) != 0xf000u )
                 regs[2] = ((regs[2] + 0x1000u) & 0xf000u) | (regs[2] & 0xffu);
--
generated by git-patchbot for /home/xen/git/xen.git#staging

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