From: Pei Li <peili.dev@gmail.com>
Date: Tue, 25 Jun 2024 20:23:10 -0700
Subject: [PATCH] kvm: Fix warning in__kvm_gpc_refresh
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Message-Id: <20240625-bug5-v1-1-e072ed5fce85@gmail.com>
To: David Woodhouse <dwmw2@infradead.org>, Paul Durrant <paul@xen.org>, 
 Sean Christopherson <seanjc@google.com>, 
 Paolo Bonzini <pbonzini@redhat.com>, Thomas Gleixner <tglx@linutronix.de>, 
 Ingo Molnar <mingo@redhat.com>, Borislav Petkov <bp@alien8.de>, 
 Dave Hansen <dave.hansen@linux.intel.com>, x86@kernel.org, 
 "H. Peter Anvin" <hpa@zytor.com>, Nathan Chancellor <nathan@kernel.org>, 
 Nick Desaulniers <ndesaulniers@google.com>, 
 Bill Wendling <morbo@google.com>, Justin Stitt <justinstitt@google.com>
Cc: kvm@vger.kernel.org, linux-kernel@vger.kernel.org, 
 skhan@linuxfoundation.org, linux-kernel-mentees@lists.linuxfoundation.org, 
 syzkaller-bugs@googlegroups.com, llvm@lists.linux.dev, 
 syzbot+fd555292a1da3180fc82@syzkaller.appspotmail.com, 
 Pei Li <peili.dev@gmail.com>

Check for invalid hva address stored in data before calling
kvm_gpc_activate_hva() instead of only compare with 0.

Reported-by: syzbot+fd555292a1da3180fc82@syzkaller.appspotmail.com
Closes: https://syzkaller.appspot.com/bug?extid=fd555292a1da3180fc82
Tested-by: syzbot+fd555292a1da3180fc82@syzkaller.appspotmail.com
Signed-off-by: Pei Li <peili.dev@gmail.com>
---
Syzbot reports a warning message in __kvm_gpc_refresh(). This warning
requires at least one of gpa and uhva to be valid.
WARNING: CPU: 0 PID: 5090 at arch/x86/kvm/../../../virt/kvm/pfncache.c:259 __kvm_gpc_refresh+0xf17/0x1090 arch/x86/kvm/../../../virt/kvm/pfncache.c:259

We are calling it from kvm_gpc_activate_hva(). This function always calls
__kvm_gpc_activate() with INVALID_GPA. Thus, uhva must be valid to
disable this warning.

This patch checks for invalid hva address as well instead of only
comparing hva with 0 before calling kvm_gpc_activate_hva()

syzbot has tested the proposed patch and the reproducer did not trigger
any issue.

Tested on:

commit:         55027e68 Merge tag 'input-for-v6.10-rc5' of git://git...
git tree:       upstream
console output: https://syzkaller.appspot.com/x/log.txt?x=16ea803a980000
kernel config:  https://syzkaller.appspot.com/x/.config?x=e40800950091403a
dashboard link: https://syzkaller.appspot.com/bug?extid=fd555292a1da3180fc82
compiler:       Debian clang version 15.0.6, GNU ld (GNU Binutils for Debian) 2.40
patch:          https://syzkaller.appspot.com/x/patch.diff?x=16eeb53e980000

Note: testing is done by a robot and is best-effort only.
---
 arch/x86/kvm/xen.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/arch/x86/kvm/xen.c b/arch/x86/kvm/xen.c
index f65b35a05d91..de5f34492405 100644
--- a/arch/x86/kvm/xen.c
+++ b/arch/x86/kvm/xen.c
@@ -881,7 +881,7 @@ int kvm_xen_vcpu_set_attr(struct kvm_vcpu *vcpu, struct kvm_xen_vcpu_attr *data)
 			r = kvm_gpc_activate(&vcpu->arch.xen.vcpu_info_cache,
 					     data->u.gpa, sizeof(struct vcpu_info));
 		} else {
-			if (data->u.hva == 0) {
+			if (data->u.hva == 0 || kvm_is_error_hva(data->u.hva)) {
 				kvm_gpc_deactivate(&vcpu->arch.xen.vcpu_info_cache);
 				r = 0;
 				break;

---
base-commit: 2bfcfd584ff5ccc8bb7acde19b42570414bf880b
change-id: 20240625-bug5-5d332b5e5161

Best regards,
-- 
Pei Li <peili.dev@gmail.com>