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target/i386: seg_helper: Correct segment selector nullification in the RET/IRET helper

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Per the SDM, when returning to outer privilege level, for segment
registers (ES, FS, GS, and DS) if the check fails, the segment
selector becomes null, but QEMU clears the base/limit/flags as well
as nullifying the segment selector, which should be a spec violation.

Real hardware seems to be compliant with the spec, at least on one
Coffee Lake board I tested.

Signed-off-by: Bin Meng <bin.meng@windriver.com>

Message-Id: <1605261378-77971-1-git-send-email-bmeng.cn@gmail.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
This commit is contained in:
Bin Meng 2020-11-13 17:56:18 +08:00 committed by Paolo Bonzini
parent c1bb5418e3
commit c2ba0515f2
1 changed files with 4 additions and 1 deletions
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5
target/i386/seg_helper.c
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@ -2108,7 +2108,10 @@ static inline void validate_seg(CPUX86State *env, int seg_reg, int cpl)
if (!(e2 & DESC_CS_MASK) || !(e2 & DESC_C_MASK)) {
/* data or non conforming code segment */
if (dpl < cpl) {
cpu_x86_load_seg_cache(env, seg_reg, 0, 0, 0, 0);
cpu_x86_load_seg_cache(env, seg_reg, 0,
env->segs[seg_reg].base,
env->segs[seg_reg].limit,
env->segs[seg_reg].flags & ~DESC_P_MASK);
}
}
}