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KVM: x86: Prioritize DR7.GD #DB over #GP due to illegal DR6/7 value

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When emulating a MOV DR, specifically a write to DR6 or DR7, treat a #DB
due to DR7.GD (General Detect) as higher priority than a #GP due to an
illegal value.  While neither Intel's SDM nor AMD's APM says anything
about the relative priority, empirical testing on Intel and AMD shows that
the #DB has higher priority.  And for VMX, where the instruction intercept
has priority over *all* exceptions, KVM already treats the #DB as having
higher priority.

Cc: Maciej W. Rozycki <macro@orcam.me.uk>
Fixes: 3b88e41a41 ("KVM: SVM: Add intercept check for accessing dr registers")
Reviewed-by: Jim Mattson <jmattson@google.com>
Link: https://patch.msgid.link/20260612230113.684301-3-seanjc@google.com
Signed-off-by: Sean Christopherson <seanjc@google.com>
This commit is contained in:
Sean Christopherson 2026-06-12 16:01:07 -07:00
parent 8f683a4dc5
commit 55ac576a9b
1 changed files with 6 additions and 1 deletions
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7
arch/x86/kvm/emulate.c
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@ -3854,11 +3854,16 @@ static int check_dr_write(struct x86_emulate_ctxt *ctxt)
{
u64 new_val = ctxt->src.val64;
int dr = ctxt->modrm_reg;
int rc;
rc = check_dr_read(ctxt);
if (rc != X86EMUL_CONTINUE)
return rc;
if ((dr == 6 || dr == 7) && (new_val & 0xffffffff00000000ULL))
return emulate_gp(ctxt, 0);
return check_dr_read(ctxt);
return X86EMUL_CONTINUE;
}
static int check_svme(struct x86_emulate_ctxt *ctxt)