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kvm: Fix warning in__kvm_gpc_refresh

PATCH Applied Pei Li 4 participants 4 messages Jun 27, 2024 – Jun 28, 2024

Subsystems (4)
x86 KVM KVM x86 KVM x86 Xen
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Pei Li

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#0 lore raw

PATCH v2 1/1 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 [email protected]
Closes https://syzkaller.appspot.com/bug?extid=fd555292a1da3180fc82
Tested-by [email protected]
Signed-off-by Pei Li <[email protected]>

---
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/[email protected]

---
 arch/x86/kvm/xen.c  | 2 +-
 virt/kvm/pfncache.c | 3 +++
 2 files changed, 4 insertions(+), 1 deletion(-)
arch/x86/kvm/xen.c +1 -1
index f65b35a05d91..67bb4e89c399 100644
@@ -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);
virt/kvm/pfncache.c +3 -0
index e3453e869e92..f0039efb9e1e 100644
@@ -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,

Signature · 1 line
Pei Li <[email protected]>
Reviewed-by on v2 1/1
#1 lore raw
Quoted 38 lines · Pei Li

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

Reported-by [email protected]
Closes https://syzkaller.appspot.com/bug?extid=fd555292a1da3180fc82
Tested-by [email protected]
Signed-off-by Pei Li <[email protected]>

---
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/[email protected]

Quoted 5 lines
---
  arch/x86/kvm/xen.c  | 2 +-
  virt/kvm/pfncache.c | 3 +++
  2 files changed, 4 insertions(+), 1 deletion(-)
Reviewed-by Paul Durrant <[email protected]>
maintainer Reviewed-by
#2 lore raw
Quoted 45 lines · Paul Durrant
Quoted 41 lines · Pei Li

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

Reported-by [email protected]
Closes https://syzkaller.appspot.com/bug?extid=fd555292a1da3180fc82
Tested-by [email protected]
Signed-off-by Pei Li <[email protected]>

---
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/[email protected]
---
  arch/x86/kvm/xen.c  | 2 +-
  virt/kvm/pfncache.c | 3 +++

Quoted 2 lines
  2 files changed, 4 insertions(+), 1 deletion(-)
Quoted 1 line
Reviewed-by Paul Durrant <[email protected]>
Reviewed-by David Woodhouse <[email protected]>

Thanks.