lists.openwall.net | lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC | |
Open Source and information security mailing list archives
| ||
|
Date: Fri, 14 Jun 2019 07:14:24 -0700 From: Sean Christopherson <sean.j.christopherson@...el.com> To: Borislav Petkov <bp@...en8.de> Cc: Fenghua Yu <fenghua.yu@...el.com>, Thomas Gleixner <tglx@...utronix.de>, Ingo Molnar <mingo@...hat.com>, H Peter Anvin <hpa@...or.com>, Ravi V Shankar <ravi.v.shankar@...el.com>, linux-kernel <linux-kernel@...r.kernel.org>, x86 <x86@...nel.org>, Radim Krčmář <rkrcmar@...hat.com>, Paolo Bonzini <pbonzini@...hat.com> Subject: Re: [RFC PATCH 2/3] x86/cpufeatures: Combine word 11 and 12 into new scattered features word 11 On Fri, Jun 14, 2019 at 03:41:23PM +0200, Borislav Petkov wrote: > + Radim and Paolo. See upthread for context. > > On Fri, Jun 14, 2019 at 06:17:02AM -0700, Fenghua Yu wrote: > > > Alternatively - and what I think is the better solution - would be to > > > remove those BUILD_BUG_ONs in x86_feature_cpuid and filter out the > > > Linux-defined leafs dynamically. This way the array won't have holes in > > > it. > > > > Maybe adding a dummy slot in cpuid_leafs in patch 0002 to avoid the > > compilation errors? > > Maybe you didn't read what you're replying to: "This way the array > won't have holes in it". Ontop of yours: > > diff --git a/arch/x86/kvm/cpuid.h b/arch/x86/kvm/cpuid.h > index d78a61408243..03d6f3f7b27c 100644 > --- a/arch/x86/kvm/cpuid.h > +++ b/arch/x86/kvm/cpuid.h > @@ -47,6 +47,7 @@ static const struct cpuid_reg reverse_cpuid[] = { > [CPUID_8000_0001_ECX] = {0x80000001, 0, CPUID_ECX}, > [CPUID_7_0_EBX] = { 7, 0, CPUID_EBX}, > [CPUID_D_1_EAX] = { 0xd, 1, CPUID_EAX}, > + [CPUID_7_1_EAX] = { 7, 1, CPUID_EAX}, > [CPUID_8000_0008_EBX] = {0x80000008, 0, CPUID_EBX}, > [CPUID_6_EAX] = { 6, 0, CPUID_EAX}, > [CPUID_8000_000A_EDX] = {0x8000000a, 0, CPUID_EDX}, > @@ -59,8 +60,9 @@ static __always_inline struct cpuid_reg x86_feature_cpuid(unsigned x86_feature) > { > unsigned x86_leaf = x86_feature / 32; > > - BUILD_BUG_ON(x86_leaf >= ARRAY_SIZE(reverse_cpuid)); > - BUILD_BUG_ON(reverse_cpuid[x86_leaf].function == 0); > + if (x86_leaf == CPUID_LNX_1 || > + x86_leaf == CPUID_LNX_4) > + return NULL; > > return reverse_cpuid[x86_leaf]; > } > > That's what I mean with filter out dynamically. This is wrong. KVM isn't complaining about shuffling the order of feature words, it's complaining that code is trying to do a reverse CPUID lookup to a feature that isn't in the reverse_cpuid table. Filtering out checks dynamically is just hiding bugs. >In function ‘x86_feature_cpuid’, > inlined from ‘guest_cpuid_get_register’ at arch/x86/kvm/cpuid.h:71:33, > inlined from ‘guest_cpuid_has’ at arch/x86/kvm/cpuid.h:100:8, > inlined from ‘kvm_get_msr_common’ at arch/x86/kvm/x86.c:2804:8: This corresponds to "guest_cpuid_has(vcpu, X86_FEATURE_ARCH_CAPABILITIES)", i.e. KVM is trying to query X86_FEATURE_ARCH_CAPABILITIES and is yelling that there is no reverse_cpuid entry for CPUID_7_EDX. The problem is that 'enum cpuid_leafs' no longer matches up with the word numbers defined in cpufeatures.h, e.g. CPUID_7_EDX == 17 or so, but the entries in cpufeatures.h defined CPUID_7_EDX flags using word 18. This patch also needs to modify NCAPINTS.
Powered by blists - more mailing lists