[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index] [Xen-devel] [PATCH] x86/emulate: Don't assume that addr_size == 32 implies protected mode
Callers of x86_emulate() generally define addr_size based on the code segment. In vm86 mode, the code segment is set by the hardware to be 16-bits; but it is entirely possible to enable protected mode, set the CS to 32-bits, and then disable protected mode. (This is commonly called "unreal mode".) But the instruction decoder only checks for protected mode when addr_size == 16. So in unreal mode, hardware will throw a #UD for VEX prefixes, but our instruction decoder will decode them, triggering an ASSERT() further on in _get_fpu(). (With debug=n the emulator will incorrectly emulate the instruction rather than throwing a #UD, but this is only a bug, not a crash, so it's not a security issue.) Teach the instruction decoder to check that we're in protected mode, even if addr_size is 32. While we're here, replace the open-coded protected mode check with in_protmode(). Signed-off-by: George Dunlap <george.dunlap@xxxxxxxxxx> --- CC: Andrew Cooper <andrew.cooper3@xxxxxxxxxx> CC: Jan Beulich <jbeulich@xxxxxxxx> --- xen/arch/x86/x86_emulate/x86_emulate.c | 5 +---- 1 file changed, 1 insertion(+), 4 deletions(-) diff --git a/xen/arch/x86/x86_emulate/x86_emulate.c b/xen/arch/x86/x86_emulate/x86_emulate.c index dfdcd6c..46232c4 100644 --- a/xen/arch/x86/x86_emulate/x86_emulate.c +++ b/xen/arch/x86/x86_emulate/x86_emulate.c @@ -2149,11 +2149,8 @@ x86_decode( default: BUG(); /* Shouldn't be possible. */ case 2: - if ( in_realmode(ctxt, ops) || (state->regs->eflags & EFLG_VM) ) - break; - /* fall through */ case 4: - if ( modrm_mod != 3 ) + if ( modrm_mod != 3 || !in_protmode(ctxt, ops) ) break; /* fall through */ case 8: -- 2.10.0 _______________________________________________ Xen-devel mailing list Xen-devel@xxxxxxxxxxxxx https://lists.xen.org/xen-devel
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