From 3376ca3f1a2075eaa23c5576c47d04d7e8a4adda Mon Sep 17 00:00:00 2001 From: Mathias Krause Date: Sat, 3 Feb 2024 13:45:20 +0100 Subject: [PATCH] KVM: x86: Fix KVM_GET_MSRS stack info leak Commit 6abe9c1386e5 ("KVM: X86: Move ignore_msrs handling upper the stack") changed the 'ignore_msrs' handling, including sanitizing return values to the caller. This was fine until commit 12bc2132b15e ("KVM: X86: Do the same ignore_msrs check for feature msrs") which allowed non-existing feature MSRs to be ignored, i.e. to not generate an error on the ioctl() level. It even tried to preserve the sanitization of the return value. However, the logic is flawed, as '*data' will be overwritten again with the uninitialized stack value of msr.data. Fix this by simplifying the logic and always initializing msr.data, vanishing the need for an additional error exit path. Fixes: 12bc2132b15e ("KVM: X86: Do the same ignore_msrs check for feature msrs") Signed-off-by: Mathias Krause Reviewed-by: Xiaoyao Li Link: https://lore.kernel.org/r/20240203124522.592778-2-minipli@grsecurity.net Signed-off-by: Sean Christopherson --- arch/x86/kvm/x86.c | 15 +++++---------- 1 file changed, 5 insertions(+), 10 deletions(-) diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c index 25bc52cdf8f4..3f6e82fd37f3 100644 --- a/arch/x86/kvm/x86.c +++ b/arch/x86/kvm/x86.c @@ -1704,22 +1704,17 @@ static int do_get_msr_feature(struct kvm_vcpu *vcpu, unsigned index, u64 *data) struct kvm_msr_entry msr; int r; + /* Unconditionally clear the output for simplicity */ + msr.data = 0; msr.index = index; r = kvm_get_msr_feature(&msr); - if (r == KVM_MSR_RET_INVALID) { - /* Unconditionally clear the output for simplicity */ - *data = 0; - if (kvm_msr_ignored_check(index, 0, false)) - r = 0; - } - - if (r) - return r; + if (r == KVM_MSR_RET_INVALID && kvm_msr_ignored_check(index, 0, false)) + r = 0; *data = msr.data; - return 0; + return r; } static bool __kvm_valid_efer(struct kvm_vcpu *vcpu, u64 efer) -- 2.25.1