* [PATCH] KVM: x86: move guest_pv_has out of user_access section
@ 2021-11-12 7:54 Paolo Bonzini
2021-11-12 8:11 ` David Woodhouse
0 siblings, 1 reply; 2+ messages in thread
From: Paolo Bonzini @ 2021-11-12 7:54 UTC (permalink / raw)
To: linux-kernel, kvm; +Cc: Stephen Rothwell, David Woodhouse
When UBSAN is enabled, the code emitted for the call to guest_pv_has
includes a call to __ubsan_handle_load_invalid_value. objtool
complains that this call happens with UACCESS enabled; to avoid
the warning, pull the calls to user_access_begin into both arms
of the "if" statement, after the check for guest_pv_has.
Reported-by: Stephen Rothwell <sfr@canb.auug.org.au>
Cc: David Woodhouse <dwmw2@infradead.org>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
---
arch/x86/kvm/x86.c | 9 ++++++---
1 file changed, 6 insertions(+), 3 deletions(-)
diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
index dd7b8b465675..dc7eb5fddfd3 100644
--- a/arch/x86/kvm/x86.c
+++ b/arch/x86/kvm/x86.c
@@ -3292,9 +3292,6 @@ static void record_steal_time(struct kvm_vcpu *vcpu)
}
st = (struct kvm_steal_time __user *)ghc->hva;
- if (!user_access_begin(st, sizeof(*st)))
- return;
-
/*
* Doing a TLB flush here, on the guest's behalf, can avoid
* expensive IPIs.
@@ -3303,6 +3300,9 @@ static void record_steal_time(struct kvm_vcpu *vcpu)
u8 st_preempted = 0;
int err = -EFAULT;
+ if (!user_access_begin(st, sizeof(*st)))
+ return;
+
asm volatile("1: xchgb %0, %2\n"
"xor %1, %1\n"
"2:\n"
@@ -3325,6 +3325,9 @@ static void record_steal_time(struct kvm_vcpu *vcpu)
if (!user_access_begin(st, sizeof(*st)))
goto dirty;
} else {
+ if (!user_access_begin(st, sizeof(*st)))
+ return;
+
unsafe_put_user(0, &st->preempted, out);
vcpu->arch.st.preempted = 0;
}
--
2.27.0
^ permalink raw reply related [flat|nested] 2+ messages in thread
* Re: [PATCH] KVM: x86: move guest_pv_has out of user_access section
2021-11-12 7:54 [PATCH] KVM: x86: move guest_pv_has out of user_access section Paolo Bonzini
@ 2021-11-12 8:11 ` David Woodhouse
0 siblings, 0 replies; 2+ messages in thread
From: David Woodhouse @ 2021-11-12 8:11 UTC (permalink / raw)
To: Paolo Bonzini, linux-kernel, kvm; +Cc: Stephen Rothwell
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On Fri, 2021-11-12 at 02:54 -0500, Paolo Bonzini wrote:
> When UBSAN is enabled, the code emitted for the call to guest_pv_has
> includes a call to __ubsan_handle_load_invalid_value. objtool
> complains that this call happens with UACCESS enabled; to avoid
> the warning, pull the calls to user_access_begin into both arms
> of the "if" statement, after the check for guest_pv_has.
>
> Reported-by: Stephen Rothwell <sfr@canb.auug.org.au>
> Cc: David Woodhouse <dwmw2@infradead.org>
> Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
Acked-by: David Woodhouse <dwmw@amazon.co.uk>
Thanks. I found a bunch of those objtool warnings during my original
experimentation and testing, but clearly missed that one. I'll turn on
CONFIG_UBSAN.
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