linux-kernel - [PATCH 1/2] KVM: Write the per-page "segment" when clearing (part of) a guest page

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Message-ID: <20240829191413.900740-2-seanjc@google.com>
Date: Thu, 29 Aug 2024 12:14:12 -0700
From: Sean Christopherson <seanjc@...gle.com>
To: Paolo Bonzini <pbonzini@...hat.com>
Cc: kvm@...r.kernel.org, linux-kernel@...r.kernel.org, zyr_ms@...look.com, 
	Sean Christopherson <seanjc@...gle.com>
Subject: [PATCH 1/2] KVM: Write the per-page "segment" when clearing (part of)
 a guest page

Pass "seg" instead of "len" when writing guest memory in kvm_clear_guest(),
as "seg" holds the number of bytes to write for the current page, while
"len" holds the total bytes remaining.

Luckily, all users of kvm_clear_guest() are guaranteed to not cross a page
boundary, and so the bug is unhittable in the current code base.

Fixes: 2f5414423ef5 ("KVM: remove kvm_clear_guest_page")
Reported-by: zyr_ms@...look.com
Closes: https://bugzilla.kernel.org/show_bug.cgi?id=219104
Signed-off-by: Sean Christopherson <seanjc@...gle.com>
---
 virt/kvm/kvm_main.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/virt/kvm/kvm_main.c b/virt/kvm/kvm_main.c
index 92901656a0d4..e036c17c4342 100644
--- a/virt/kvm/kvm_main.c
+++ b/virt/kvm/kvm_main.c
@@ -3582,7 +3582,7 @@ int kvm_clear_guest(struct kvm *kvm, gpa_t gpa, unsigned long len)
 	int ret;
 
 	while ((seg = next_segment(len, offset)) != 0) {
-		ret = kvm_write_guest_page(kvm, gfn, zero_page, offset, len);
+		ret = kvm_write_guest_page(kvm, gfn, zero_page, offset, seg);
 		if (ret < 0)
 			return ret;
 		offset = 0;
-- 
2.46.0.469.g59c65b2a67-goog