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[4.4] KVM: x86: Fix misplaced backport of "work around leak of uninitialized stack contents"

Message ID 1643735871-15065-1-git-send-email-guillaume.bertholon@ens.fr
State New
Headers show
Series [4.4] KVM: x86: Fix misplaced backport of "work around leak of uninitialized stack contents" | expand

Commit Message

Guillaume Bertholon Feb. 1, 2022, 5:17 p.m. UTC 
The upstream commit 541ab2aeb282 ("KVM: x86: work around leak of
uninitialized stack contents") resets `exception` in the function
`kvm_write_guest_virt_system`.
However, its backported version in stable (commit ba7f1c934f2e
("KVM: x86: work around leak of uninitialized stack contents")) applied
the change in `emulator_write_std` instead.

This patch moves the memset instruction back to
`kvm_write_guest_virt_system`.

Fixes: ba7f1c934f2e ("KVM: x86: work around leak of uninitialized stack contents")
Signed-off-by: Guillaume Bertholon <guillaume.bertholon@ens.fr>
---
 arch/x86/kvm/x86.c | 14 +++++++-------
 1 file changed, 7 insertions(+), 7 deletions(-)

--
2.7.4
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Patch

diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
index 8dce61c..9101002 100644
--- a/arch/x86/kvm/x86.c
+++ b/arch/x86/kvm/x86.c
@@ -4417,13 +4417,6 @@  static int emulator_write_std(struct x86_emulate_ctxt *ctxt, gva_t addr, void *v
 	if (!system && kvm_x86_ops->get_cpl(vcpu) == 3)
 		access |= PFERR_USER_MASK;

-	/*
-	 * FIXME: this should call handle_emulation_failure if X86EMUL_IO_NEEDED
-	 * is returned, but our callers are not ready for that and they blindly
-	 * call kvm_inject_page_fault.  Ensure that they at least do not leak
-	 * uninitialized kernel stack memory into cr2 and error code.
-	 */
-	memset(exception, 0, sizeof(*exception));
 	return kvm_write_guest_virt_helper(addr, val, bytes, vcpu,
 					   access, exception);
 }
@@ -4431,6 +4424,13 @@  static int emulator_write_std(struct x86_emulate_ctxt *ctxt, gva_t addr, void *v
 int kvm_write_guest_virt_system(struct kvm_vcpu *vcpu, gva_t addr, void *val,
 				unsigned int bytes, struct x86_exception *exception)
 {
+	/*
+	 * FIXME: this should call handle_emulation_failure if X86EMUL_IO_NEEDED
+	 * is returned, but our callers are not ready for that and they blindly
+	 * call kvm_inject_page_fault.  Ensure that they at least do not leak
+	 * uninitialized kernel stack memory into cr2 and error code.
+	 */
+	memset(exception, 0, sizeof(*exception));
 	return kvm_write_guest_virt_helper(addr, val, bytes, vcpu,
 					   PFERR_WRITE_MASK, exception);
 }