linux-kernel - [PATCH 5.14 793/849] KVM: x86: move guest_pv_has out of user

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Message-Id: <20211115165447.068593140@linuxfoundation.org>
Date:   Mon, 15 Nov 2021 18:04:36 +0100
From:   Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:     linux-kernel@...r.kernel.org
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        stable@...r.kernel.org, Stephen Rothwell <sfr@...b.auug.org.au>,
        David Woodhouse <dwmw2@...radead.org>,
        Paolo Bonzini <pbonzini@...hat.com>
Subject: [PATCH 5.14 793/849] KVM: x86: move guest_pv_has out of user_access section

From: Paolo Bonzini <pbonzini@...hat.com>

commit 3e067fd8503d6205aa0c1c8f48f6b209c592d19c upstream.

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@...b.auug.org.au>
Cc: David Woodhouse <dwmw2@...radead.org>
Signed-off-by: Paolo Bonzini <pbonzini@...hat.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
---
 arch/x86/kvm/x86.c |    9 ++++++---
 1 file changed, 6 insertions(+), 3 deletions(-)

--- a/arch/x86/kvm/x86.c
+++ b/arch/x86/kvm/x86.c
@@ -3222,9 +3222,6 @@ static void record_steal_time(struct kvm
 	}
 
 	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.
@@ -3233,6 +3230,9 @@ static void record_steal_time(struct kvm
 		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"
@@ -3255,6 +3255,9 @@ static void record_steal_time(struct kvm
 		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;
 	}