[PATCH] qemu-kvm: Work around borken MSR_GET_INDEX_LIST

From: Jan Kiszka <jan.kiszka@web.de>
To: Avi Kivity <avi@redhat.com>
Cc: kvm-devel <kvm@vger.kernel.org>
Subject: [PATCH] qemu-kvm: Work around borken MSR_GET_INDEX_LIST
Date: Thu, 02 Jul 2009 21:50:49 +0200	[thread overview]
Message-ID: <4A4D0F99.2030604@web.de> (raw)

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Allocate enough memory for KVM_GET_MSR_INDEX_LIST as older kernels shot
far beyond their limits, corrupting user space memory.

Signed-off-by: Jan Kiszka <jan.kiszka@siemens.com>
---

 qemu-kvm-x86.c |    5 ++++-
 1 files changed, 4 insertions(+), 1 deletions(-)

diff --git a/qemu-kvm-x86.c b/qemu-kvm-x86.c
index d6735c1..e528acb 100644
--- a/qemu-kvm-x86.c
+++ b/qemu-kvm-x86.c
@@ -349,7 +349,10 @@ struct kvm_msr_list *kvm_get_msr_list(kvm_context_t kvm)
 	r = ioctl(kvm->fd, KVM_GET_MSR_INDEX_LIST, &sizer);
 	if (r == -1 && errno != E2BIG)
 		return NULL;
-	msrs = malloc(sizeof *msrs + sizer.nmsrs * sizeof *msrs->indices);
+	/* Old kernel modules had a bug and could write beyond the provided
+	   memory. Allocate at least a safe amount of 1K. */
+	msrs = malloc(MAX(1024, sizeof(*msrs) +
+				sizer.nmsrs * sizeof(*msrs->indices)));
 	if (!msrs) {
 		errno = ENOMEM;
 		return NULL;


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