* [PATCH v2 1/3] KVM: x86/emulator: Defer not-present segment check in __load_segment_descriptor()
[not found] <cover.1644292363.git.houwenlong.hwl@antgroup.com>
@ 2022-02-08 9:34 ` Hou Wenlong
2022-02-08 9:34 ` [PATCH v2 2/3] KVM: x86/emulator: Fix wrong privilege check for code segment " Hou Wenlong
2022-02-08 9:34 ` [PATCH v2 3/3] KVM: x86/emulator: Move the unhandled outer privilege level logic of far return into __load_segment_descriptor() Hou Wenlong
2 siblings, 0 replies; 4+ messages in thread
From: Hou Wenlong @ 2022-02-08 9:34 UTC (permalink / raw)
To: kvm
Cc: Sean Christopherson, Paolo Bonzini, Vitaly Kuznetsov, Wanpeng Li,
Jim Mattson, Joerg Roedel, Thomas Gleixner, Ingo Molnar,
Borislav Petkov, Dave Hansen, x86, H. Peter Anvin,
Marcelo Tosatti, Gleb Natapov, linux-kernel
Per Intel's SDM on the "Instruction Set Reference", when
loading segment descriptor, not-present segment check should
be after all type and privilege checks. But the emulator checks
it first, then #NP is triggered instead of #GP if privilege fails
and segment is not present. Put not-present segment check after
type and privilege checks in __load_segment_descriptor().
Fixes: 38ba30ba51a00 (KVM: x86 emulator: Emulate task switch in emulator.c)
Reviewed-by: Sean Christopherson <seanjc@google.com>
Signed-off-by: Hou Wenlong <houwenlong.hwl@antgroup.com>
---
arch/x86/kvm/emulate.c | 14 +++++++++-----
1 file changed, 9 insertions(+), 5 deletions(-)
diff --git a/arch/x86/kvm/emulate.c b/arch/x86/kvm/emulate.c
index 9e4a00d04532..b7ee7de9f8cd 100644
--- a/arch/x86/kvm/emulate.c
+++ b/arch/x86/kvm/emulate.c
@@ -1616,11 +1616,6 @@ static int __load_segment_descriptor(struct x86_emulate_ctxt *ctxt,
goto exception;
}
- if (!seg_desc.p) {
- err_vec = (seg == VCPU_SREG_SS) ? SS_VECTOR : NP_VECTOR;
- goto exception;
- }
-
dpl = seg_desc.dpl;
switch (seg) {
@@ -1660,6 +1655,10 @@ static int __load_segment_descriptor(struct x86_emulate_ctxt *ctxt,
case VCPU_SREG_TR:
if (seg_desc.s || (seg_desc.type != 1 && seg_desc.type != 9))
goto exception;
+ if (!seg_desc.p) {
+ err_vec = NP_VECTOR;
+ goto exception;
+ }
old_desc = seg_desc;
seg_desc.type |= 2; /* busy */
ret = ctxt->ops->cmpxchg_emulated(ctxt, desc_addr, &old_desc, &seg_desc,
@@ -1684,6 +1683,11 @@ static int __load_segment_descriptor(struct x86_emulate_ctxt *ctxt,
break;
}
+ if (!seg_desc.p) {
+ err_vec = (seg == VCPU_SREG_SS) ? SS_VECTOR : NP_VECTOR;
+ goto exception;
+ }
+
if (seg_desc.s) {
/* mark segment as accessed */
if (!(seg_desc.type & 1)) {
--
2.31.1
^ permalink raw reply [flat|nested] 4+ messages in thread* [PATCH v2 2/3] KVM: x86/emulator: Fix wrong privilege check for code segment in __load_segment_descriptor()
[not found] <cover.1644292363.git.houwenlong.hwl@antgroup.com>
2022-02-08 9:34 ` [PATCH v2 1/3] KVM: x86/emulator: Defer not-present segment check in __load_segment_descriptor() Hou Wenlong
@ 2022-02-08 9:34 ` Hou Wenlong
2022-02-08 9:34 ` [PATCH v2 3/3] KVM: x86/emulator: Move the unhandled outer privilege level logic of far return into __load_segment_descriptor() Hou Wenlong
2 siblings, 0 replies; 4+ messages in thread
From: Hou Wenlong @ 2022-02-08 9:34 UTC (permalink / raw)
To: kvm
Cc: Sean Christopherson, Paolo Bonzini, Vitaly Kuznetsov, Wanpeng Li,
Jim Mattson, Joerg Roedel, Thomas Gleixner, Ingo Molnar,
Borislav Petkov, Dave Hansen, x86, H. Peter Anvin, linux-kernel
Code segment descriptor can be loaded by jmp/call/ret, iret
and int. The privilege checks are different between those
instructions above realmode. Although, the emulator has
use x86_transfer_type enumerate to differentiate them, but
it is not really used in __load_segment_descriptor(). Note,
far jump/call to call gate, task gate or task state segment
are not implemented in emulator.
As for far jump/call to code segment, if DPL > CPL for conforming
code or (RPL > CPL or DPL != CPL) for non-conforming code, it
should trigger #GP. The current checks are ok.
As for far return, if RPL < CPL or DPL > RPL for conforming
code or DPL != RPL for non-conforming code, it should trigger #GP.
Outer level return is not implemented above virtual-8086 mode in
emulator. So it implies that RPL <= CPL, but the current checks
wouldn't trigger #GP if RPL < CPL.
As for code segment loading in task switch, if DPL > RPL for conforming
code or DPL != RPL for non-conforming code, it should trigger #TS. Since
segment selector is loaded before segment descriptor when load state from
tss, it implies that RPL = CPL, so the current checks are ok.
The only problem in current implementation is missing RPL < CPL check for
far return. However, change code to follow the manual is better.
Reviewed-by: Sean Christopherson <seanjc@google.com>
Signed-off-by: Hou Wenlong <houwenlong.hwl@antgroup.com>
---
arch/x86/kvm/emulate.c | 31 +++++++++++++++++++++++--------
1 file changed, 23 insertions(+), 8 deletions(-)
diff --git a/arch/x86/kvm/emulate.c b/arch/x86/kvm/emulate.c
index b7ee7de9f8cd..37c4213bdcc1 100644
--- a/arch/x86/kvm/emulate.c
+++ b/arch/x86/kvm/emulate.c
@@ -1631,14 +1631,29 @@ static int __load_segment_descriptor(struct x86_emulate_ctxt *ctxt,
if (!(seg_desc.type & 8))
goto exception;
- if (seg_desc.type & 4) {
- /* conforming */
- if (dpl > cpl)
- goto exception;
- } else {
- /* nonconforming */
- if (rpl > cpl || dpl != cpl)
- goto exception;
+ /* RET can never return to an inner privilege level. */
+ if (transfer == X86_TRANSFER_RET && rpl < cpl)
+ goto exception;
+ if (transfer == X86_TRANSFER_RET || transfer == X86_TRANSFER_TASK_SWITCH) {
+ if (seg_desc.type & 4) {
+ /* conforming */
+ if (dpl > rpl)
+ goto exception;
+ } else {
+ /* nonconforming */
+ if (dpl != rpl)
+ goto exception;
+ }
+ } else { /* X86_TRANSFER_CALL_JMP */
+ if (seg_desc.type & 4) {
+ /* conforming */
+ if (dpl > cpl)
+ goto exception;
+ } else {
+ /* nonconforming */
+ if (rpl > cpl || dpl != cpl)
+ goto exception;
+ }
}
/* in long-mode d/b must be clear if l is set */
if (seg_desc.d && seg_desc.l) {
--
2.31.1
^ permalink raw reply [flat|nested] 4+ messages in thread* [PATCH v2 3/3] KVM: x86/emulator: Move the unhandled outer privilege level logic of far return into __load_segment_descriptor()
[not found] <cover.1644292363.git.houwenlong.hwl@antgroup.com>
2022-02-08 9:34 ` [PATCH v2 1/3] KVM: x86/emulator: Defer not-present segment check in __load_segment_descriptor() Hou Wenlong
2022-02-08 9:34 ` [PATCH v2 2/3] KVM: x86/emulator: Fix wrong privilege check for code segment " Hou Wenlong
@ 2022-02-08 9:34 ` Hou Wenlong
2022-02-25 15:07 ` Paolo Bonzini
2 siblings, 1 reply; 4+ messages in thread
From: Hou Wenlong @ 2022-02-08 9:34 UTC (permalink / raw)
To: kvm
Cc: Sean Christopherson, Paolo Bonzini, Vitaly Kuznetsov, Wanpeng Li,
Jim Mattson, Joerg Roedel, Thomas Gleixner, Ingo Molnar,
Borislav Petkov, Dave Hansen, x86, H. Peter Anvin, linux-kernel
Outer-privilege level return is not implemented in emulator,
move the unhandled logic into __load_segment_descriptor to
make it easier to understand why the checks for RET are
incomplete.
Suggested-by: Sean Christopherson <seanjc@google.com>
Signed-off-by: Hou Wenlong <houwenlong.hwl@antgroup.com>
---
arch/x86/kvm/emulate.c | 14 ++++++++------
1 file changed, 8 insertions(+), 6 deletions(-)
diff --git a/arch/x86/kvm/emulate.c b/arch/x86/kvm/emulate.c
index 37c4213bdcc1..bd91b952eb0a 100644
--- a/arch/x86/kvm/emulate.c
+++ b/arch/x86/kvm/emulate.c
@@ -1631,9 +1631,14 @@ static int __load_segment_descriptor(struct x86_emulate_ctxt *ctxt,
if (!(seg_desc.type & 8))
goto exception;
- /* RET can never return to an inner privilege level. */
- if (transfer == X86_TRANSFER_RET && rpl < cpl)
- goto exception;
+ if (transfer == X86_TRANSFER_RET) {
+ /* RET can never return to an inner privilege level. */
+ if (rpl < cpl)
+ goto exception;
+ /* Outer-privilege level return is not implemented */
+ if (rpl > cpl)
+ return X86EMUL_UNHANDLEABLE;
+ }
if (transfer == X86_TRANSFER_RET || transfer == X86_TRANSFER_TASK_SWITCH) {
if (seg_desc.type & 4) {
/* conforming */
@@ -2228,9 +2233,6 @@ static int em_ret_far(struct x86_emulate_ctxt *ctxt)
rc = emulate_pop(ctxt, &cs, ctxt->op_bytes);
if (rc != X86EMUL_CONTINUE)
return rc;
- /* Outer-privilege level return is not implemented */
- if (ctxt->mode >= X86EMUL_MODE_PROT16 && (cs & 3) > cpl)
- return X86EMUL_UNHANDLEABLE;
rc = __load_segment_descriptor(ctxt, (u16)cs, VCPU_SREG_CS, cpl,
X86_TRANSFER_RET,
&new_desc);
--
2.31.1
^ permalink raw reply [flat|nested] 4+ messages in thread* Re: [PATCH v2 3/3] KVM: x86/emulator: Move the unhandled outer privilege level logic of far return into __load_segment_descriptor()
2022-02-08 9:34 ` [PATCH v2 3/3] KVM: x86/emulator: Move the unhandled outer privilege level logic of far return into __load_segment_descriptor() Hou Wenlong
@ 2022-02-25 15:07 ` Paolo Bonzini
0 siblings, 0 replies; 4+ messages in thread
From: Paolo Bonzini @ 2022-02-25 15:07 UTC (permalink / raw)
To: Hou Wenlong, kvm
Cc: Sean Christopherson, Vitaly Kuznetsov, Wanpeng Li, Jim Mattson,
Joerg Roedel, Thomas Gleixner, Ingo Molnar, Borislav Petkov,
Dave Hansen, x86, H. Peter Anvin, linux-kernel
On 2/8/22 10:34, Hou Wenlong wrote:
> Outer-privilege level return is not implemented in emulator,
> move the unhandled logic into __load_segment_descriptor to
> make it easier to understand why the checks for RET are
> incomplete.
>
> Suggested-by: Sean Christopherson <seanjc@google.com>
> Signed-off-by: Hou Wenlong <houwenlong.hwl@antgroup.com>
> ---
> arch/x86/kvm/emulate.c | 14 ++++++++------
> 1 file changed, 8 insertions(+), 6 deletions(-)
>
> diff --git a/arch/x86/kvm/emulate.c b/arch/x86/kvm/emulate.c
> index 37c4213bdcc1..bd91b952eb0a 100644
> --- a/arch/x86/kvm/emulate.c
> +++ b/arch/x86/kvm/emulate.c
> @@ -1631,9 +1631,14 @@ static int __load_segment_descriptor(struct x86_emulate_ctxt *ctxt,
> if (!(seg_desc.type & 8))
> goto exception;
>
> - /* RET can never return to an inner privilege level. */
> - if (transfer == X86_TRANSFER_RET && rpl < cpl)
> - goto exception;
> + if (transfer == X86_TRANSFER_RET) {
> + /* RET can never return to an inner privilege level. */
> + if (rpl < cpl)
> + goto exception;
> + /* Outer-privilege level return is not implemented */
> + if (rpl > cpl)
> + return X86EMUL_UNHANDLEABLE;
> + }
> if (transfer == X86_TRANSFER_RET || transfer == X86_TRANSFER_TASK_SWITCH) {
> if (seg_desc.type & 4) {
> /* conforming */
> @@ -2228,9 +2233,6 @@ static int em_ret_far(struct x86_emulate_ctxt *ctxt)
> rc = emulate_pop(ctxt, &cs, ctxt->op_bytes);
> if (rc != X86EMUL_CONTINUE)
> return rc;
> - /* Outer-privilege level return is not implemented */
> - if (ctxt->mode >= X86EMUL_MODE_PROT16 && (cs & 3) > cpl)
> - return X86EMUL_UNHANDLEABLE;
> rc = __load_segment_descriptor(ctxt, (u16)cs, VCPU_SREG_CS, cpl,
> X86_TRANSFER_RET,
> &new_desc);
Queued all three, thanks!
Paolo
^ permalink raw reply [flat|nested] 4+ messages in thread