From 798d8ec0dacd4cc0034298d94f430c14f23e2919 Mon Sep 17 00:00:00 2001 From: Paolo Bonzini Date: Fri, 29 Apr 2022 21:16:28 +0200 Subject: [PATCH] target/i386: do not consult nonexistent host leaves When cache_info_passthrough is requested, QEMU passes the host values of the cache information CPUID leaves down to the guest. However, it blindly assumes that the CPUID leaf exists on the host, and this cannot be guaranteed: for example, KVM has recently started to synthesize AMD leaves up to 0x80000021 in order to provide accurate CPU bug information to guests. Querying a nonexistent host leaf fills the output arguments of host_cpuid with data that (albeit deterministic) is nonsensical as cache information, namely the data in the highest Intel CPUID leaf. If said highest leaf is not ECX-dependent, this can even cause an infinite loop when kvm_arch_init_vcpu prepares the input to KVM_SET_CPUID2. The infinite loop is only terminated by an abort() when the array gets full. Reported-by: Maxim Levitsky Reviewed-by: Maxim Levitsky Cc: qemu-stable@nongnu.org Signed-off-by: Paolo Bonzini --- target/i386/cpu.c | 41 ++++++++++++++++++++++++++++++++++++----- 1 file changed, 36 insertions(+), 5 deletions(-) diff --git a/target/i386/cpu.c b/target/i386/cpu.c index 62c240fa91..c4a17c93f6 100644 --- a/target/i386/cpu.c +++ b/target/i386/cpu.c @@ -5022,6 +5022,37 @@ uint64_t x86_cpu_get_supported_feature_word(FeatureWord w, return r; } +static void x86_cpu_get_cache_cpuid(uint32_t func, uint32_t index, + uint32_t *eax, uint32_t *ebx, + uint32_t *ecx, uint32_t *edx) +{ + uint32_t level, unused; + + /* Only return valid host leaves. */ + switch (func) { + case 2: + case 4: + host_cpuid(0, 0, &level, &unused, &unused, &unused); + break; + case 0x80000005: + case 0x80000006: + case 0x8000001d: + host_cpuid(0x80000000, 0, &level, &unused, &unused, &unused); + break; + default: + return; + } + + if (func > level) { + *eax = 0; + *ebx = 0; + *ecx = 0; + *edx = 0; + } else { + host_cpuid(func, index, eax, ebx, ecx, edx); + } +} + /* * Only for builtin_x86_defs models initialized with x86_register_cpudef_types. */ @@ -5280,7 +5311,7 @@ void cpu_x86_cpuid(CPUX86State *env, uint32_t index, uint32_t count, case 2: /* cache info: needed for Pentium Pro compatibility */ if (cpu->cache_info_passthrough) { - host_cpuid(index, 0, eax, ebx, ecx, edx); + x86_cpu_get_cache_cpuid(index, 0, eax, ebx, ecx, edx); break; } else if (cpu->vendor_cpuid_only && IS_AMD_CPU(env)) { *eax = *ebx = *ecx = *edx = 0; @@ -5300,7 +5331,7 @@ void cpu_x86_cpuid(CPUX86State *env, uint32_t index, uint32_t count, case 4: /* cache info: needed for Core compatibility */ if (cpu->cache_info_passthrough) { - host_cpuid(index, count, eax, ebx, ecx, edx); + x86_cpu_get_cache_cpuid(index, count, eax, ebx, ecx, edx); /* QEMU gives out its own APIC IDs, never pass down bits 31..26. */ *eax &= ~0xFC000000; if ((*eax & 31) && cs->nr_cores > 1) { @@ -5702,7 +5733,7 @@ void cpu_x86_cpuid(CPUX86State *env, uint32_t index, uint32_t count, case 0x80000005: /* cache info (L1 cache) */ if (cpu->cache_info_passthrough) { - host_cpuid(index, 0, eax, ebx, ecx, edx); + x86_cpu_get_cache_cpuid(index, 0, eax, ebx, ecx, edx); break; } *eax = (L1_DTLB_2M_ASSOC << 24) | (L1_DTLB_2M_ENTRIES << 16) | @@ -5715,7 +5746,7 @@ void cpu_x86_cpuid(CPUX86State *env, uint32_t index, uint32_t count, case 0x80000006: /* cache info (L2 cache) */ if (cpu->cache_info_passthrough) { - host_cpuid(index, 0, eax, ebx, ecx, edx); + x86_cpu_get_cache_cpuid(index, 0, eax, ebx, ecx, edx); break; } *eax = (AMD_ENC_ASSOC(L2_DTLB_2M_ASSOC) << 28) | @@ -5775,7 +5806,7 @@ void cpu_x86_cpuid(CPUX86State *env, uint32_t index, uint32_t count, case 0x8000001D: *eax = 0; if (cpu->cache_info_passthrough) { - host_cpuid(index, count, eax, ebx, ecx, edx); + x86_cpu_get_cache_cpuid(index, count, eax, ebx, ecx, edx); break; } switch (count) {