[PATCH] KVM: arm64: nested: Fix VA sign extension in VNCR/TLBI paths

[PATCH] KVM: arm64: nested: Fix VA sign extension in VNCR/TLBI paths

[Gyujeong Jin]

From: gyutrange <wlsrbwjd643@naver.com>

VNCR/TLBI VA reconstruction currently uses bit 48 as the sign bit,
but for 48-bit virtual addresses the correct sign bit is bit 47.
Using 48 can mis-canonicalize addresses in the negative half and may
cause missed invalidations.

Although VNCR_EL2 encodes other architectural fields (RESS, BADDR;
see Arm ARM D24.2.206), sign_extend64() interprets its second argument
as the index of the sign bit. Passing 48 prevents propagation of the
canonical sign bit for 48-bit VAs.

Impact:
- Incorrect canonicalization of VAs with bit47=1
- Potential stale VNCR pseudo-TLB entries after TLBI or MMU notifier
- Possible incorrect translation/permissions or DoS when combined
  with other issues

Fixes: 667304740537 ("KVM: arm64: Mask out non-VA bits from TLBI VA* on VNCR invalidation")
Cc: stable@vger.kernel.org
Reported-by: DongHa Lee <gap-dev@example.com>
Reported-by: Gyujeong Jin <wlsrbwjd7232@gmail.com>
Reported-by: Daehyeon Ko <4ncient@example.com>
Reported-by: Geonha Lee <leegn4a@example.com>
Reported-by: Hyungyu Oh <dqpc_lover@example.com>
Reported-by: Jaewon Yang <r4mbb1@example.com>
Signed-off-by: Gyujeong Jin <wlsrbwjd7232@gmail.com>
---
 arch/arm64/kvm/nested.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/arch/arm64/kvm/nested.c b/arch/arm64/kvm/nested.c
index 77db81bae86f..eaa6dd9da086 100644
--- a/arch/arm64/kvm/nested.c
+++ b/arch/arm64/kvm/nested.c
@@ -1169,7 +1169,7 @@ int kvm_vcpu_allocate_vncr_tlb(struct kvm_vcpu *vcpu)
 
 static u64 read_vncr_el2(struct kvm_vcpu *vcpu)
 {
-	return (u64)sign_extend64(__vcpu_sys_reg(vcpu, VNCR_EL2), 48);
+	return (u64)sign_extend64(__vcpu_sys_reg(vcpu, VNCR_EL2), 47);
 }
 
 static int kvm_translate_vncr(struct kvm_vcpu *vcpu)
-- 
2.43.0

Re: [PATCH] KVM: arm64: nested: Fix VA sign extension in VNCR/TLBI paths

[Marc Zyngier]

On Mon, 01 Sep 2025 15:15:51 +0100,
Gyujeong Jin <wlsrbwjd7232@gmail.com> wrote:
> 
> From: gyutrange <wlsrbwjd643@naver.com>
> 
> VNCR/TLBI VA reconstruction currently uses bit 48 as the sign bit,
> but for 48-bit virtual addresses the correct sign bit is bit 47.

No, that's not the case. Bit 55 is used at all times to determine
which half of the address space a VA gets resolved from.

> Using 48 can mis-canonicalize addresses in the negative half and may
> cause missed invalidations.
> 
> Although VNCR_EL2 encodes other architectural fields (RESS, BADDR;
> see Arm ARM D24.2.206), sign_extend64() interprets its second argument
> as the index of the sign bit. Passing 48 prevents propagation of the
> canonical sign bit for 48-bit VAs.
> 
> Impact:
> - Incorrect canonicalization of VAs with bit47=1

No. We are not trying to make the VA canonical.

> - Potential stale VNCR pseudo-TLB entries after TLBI or MMU notifier

No. The pseudo TLB is never created the first place.

> - Possible incorrect translation/permissions or DoS when combined
>   with other issues

Please explain, as "other issues" is not a valid argument.

Thanks,

	M.

-- 
Without deviation from the norm, progress is not possible.

Re: [PATCH] KVM: arm64: nested: Fix VA sign extension in VNCR/TLBI paths

[Greg KH]

On Mon, Sep 01, 2025 at 11:15:51PM +0900, Gyujeong Jin wrote:
> From: gyutrange <wlsrbwjd643@naver.com>

Does not match your signed-off-by line :(

Re: [PATCH] KVM: arm64: nested: Fix VA sign extension in VNCR/TLBI paths

[Greg KH]

On Mon, Sep 01, 2025 at 11:15:51PM +0900, Gyujeong Jin wrote:
> From: gyutrange <wlsrbwjd643@naver.com>
> 
> VNCR/TLBI VA reconstruction currently uses bit 48 as the sign bit,
> but for 48-bit virtual addresses the correct sign bit is bit 47.
> Using 48 can mis-canonicalize addresses in the negative half and may
> cause missed invalidations.
> 
> Although VNCR_EL2 encodes other architectural fields (RESS, BADDR;
> see Arm ARM D24.2.206), sign_extend64() interprets its second argument
> as the index of the sign bit. Passing 48 prevents propagation of the
> canonical sign bit for 48-bit VAs.
> 
> Impact:
> - Incorrect canonicalization of VAs with bit47=1
> - Potential stale VNCR pseudo-TLB entries after TLBI or MMU notifier
> - Possible incorrect translation/permissions or DoS when combined
>   with other issues
> 
> Fixes: 667304740537 ("KVM: arm64: Mask out non-VA bits from TLBI VA* on VNCR invalidation")
> Cc: stable@vger.kernel.org
> Reported-by: DongHa Lee <gap-dev@example.com>
> Reported-by: Gyujeong Jin <wlsrbwjd7232@gmail.com>
> Reported-by: Daehyeon Ko <4ncient@example.com>
> Reported-by: Geonha Lee <leegn4a@example.com>
> Reported-by: Hyungyu Oh <dqpc_lover@example.com>
> Reported-by: Jaewon Yang <r4mbb1@example.com>

Please do not use fake email addresses.