linux-kernel - [PATCH v2] kvm: Fix warning in__kvm_gpc

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Date: Thu, 27 Jun 2024 08:03:56 -0700
From: Pei Li <peili.dev@...il.com>
To: David Woodhouse <dwmw2@...radead.org>, Paul Durrant <paul@....org>, 
 Sean Christopherson <seanjc@...gle.com>, 
 Paolo Bonzini <pbonzini@...hat.com>, Thomas Gleixner <tglx@...utronix.de>, 
 Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>, 
 Dave Hansen <dave.hansen@...ux.intel.com>, x86@...nel.org, 
 "H. Peter Anvin" <hpa@...or.com>, Nathan Chancellor <nathan@...nel.org>, 
 Nick Desaulniers <ndesaulniers@...gle.com>, 
 Bill Wendling <morbo@...gle.com>, Justin Stitt <justinstitt@...gle.com>
Cc: kvm@...r.kernel.org, linux-kernel@...r.kernel.org, 
 skhan@...uxfoundation.org, linux-kernel-mentees@...ts.linuxfoundation.org, 
 syzkaller-bugs@...glegroups.com, llvm@...ts.linux.dev, 
 syzbot+fd555292a1da3180fc82@...kaller.appspotmail.com, 
 Pei Li <peili.dev@...il.com>
Subject: [PATCH v2] kvm: Fix warning in__kvm_gpc_refresh

Check for invalid hva address stored in data and return -EINVAL before
calling into __kvm_gpc_activate().

Reported-by: syzbot+fd555292a1da3180fc82@...kaller.appspotmail.com
Closes: https://syzkaller.appspot.com/bug?extid=fd555292a1da3180fc82
Tested-by: syzbot+fd555292a1da3180fc82@...kaller.appspotmail.com
Signed-off-by: Pei Li <peili.dev@...il.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 and return -EINVAL before
calling __kvm_gpc_activate().

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

Tested on:

commit:         afcd4813 Merge tag 'mm-hotfixes-stable-2024-06-26-17-2..
git tree:       upstream
console output: https://syzkaller.appspot.com/x/log.txt?x=1427e301980000
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=13838f3e980000

Note: testing is done by a robot and is best-effort only.
---
Changes in v2:
- Adapted Sean's suggestion to check for valid address before calling
  into __kvm_gpc_activate().
- Link to v1: https://lore.kernel.org/r/20240625-bug5-v1-1-e072ed5fce85@gmail.com
---
 arch/x86/kvm/xen.c  | 2 +-
 virt/kvm/pfncache.c | 3 +++
 2 files changed, 4 insertions(+), 1 deletion(-)

diff --git a/arch/x86/kvm/xen.c b/arch/x86/kvm/xen.c
index f65b35a05d91..67bb4e89c399 100644
--- a/arch/x86/kvm/xen.c
+++ b/arch/x86/kvm/xen.c
@@ -741,7 +741,7 @@ int kvm_xen_hvm_set_attr(struct kvm *kvm, struct kvm_xen_hvm_attr *data)
 		} else {
 			void __user * hva = u64_to_user_ptr(data->u.shared_info.hva);

-			if (!PAGE_ALIGNED(hva) || !access_ok(hva, PAGE_SIZE)) {
+			if (!PAGE_ALIGNED(hva)) {
 				r = -EINVAL;
 			} else if (!hva) {
 				kvm_gpc_deactivate(&kvm->arch.xen.shinfo_cache);
diff --git a/virt/kvm/pfncache.c b/virt/kvm/pfncache.c
index e3453e869e92..f0039efb9e1e 100644
--- a/virt/kvm/pfncache.c
+++ b/virt/kvm/pfncache.c
@@ -430,6 +430,9 @@ int kvm_gpc_activate(struct gfn_to_pfn_cache *gpc, gpa_t gpa, unsigned long len)

 int kvm_gpc_activate_hva(struct gfn_to_pfn_cache *gpc, unsigned long uhva, unsigned long len)
 {
+	if (!access_ok((void __user *)uhva, len))
+		return -EINVAL;
+
 	return __kvm_gpc_activate(gpc, INVALID_GPA, uhva, len);
 }

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

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