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Date: Tue, 15 Jul 2014 19:48:10 -0700 From: Andy Lutomirski <luto@...capital.net> To: kvm@...r.kernel.org, "H. Peter Anvin" <hpa@...or.com>, Theodore Ts'o <tytso@....edu>, linux-kernel@...r.kernel.org, Kees Cook <keescook@...omium.org>, x86@...nel.org Cc: Daniel Borkmann <dborkman@...hat.com>, Srivatsa Vaddagiri <vatsa@...ux.vnet.ibm.com>, Raghavendra K T <raghavendra.kt@...ux.vnet.ibm.com>, Andy Lutomirski <luto@...capital.net> Subject: [PATCH 4/4] x86,kaslr: Use MSR_KVM_GET_RNG_SEED for KASLR if available It's considerably better than any of the alternatives on KVM. Signed-off-by: Andy Lutomirski <luto@...capital.net> --- arch/x86/boot/compressed/aslr.c | 27 +++++++++++++++++++++++++++ 1 file changed, 27 insertions(+) diff --git a/arch/x86/boot/compressed/aslr.c b/arch/x86/boot/compressed/aslr.c index fc6091a..8583f0e 100644 --- a/arch/x86/boot/compressed/aslr.c +++ b/arch/x86/boot/compressed/aslr.c @@ -5,6 +5,8 @@ #include <asm/archrandom.h> #include <asm/e820.h> +#include <uapi/asm/kvm_para.h> + #include <generated/compile.h> #include <linux/module.h> #include <linux/uts.h> @@ -15,6 +17,22 @@ static const char build_str[] = UTS_RELEASE " (" LINUX_COMPILE_BY "@" LINUX_COMPILE_HOST ") (" LINUX_COMPILER ") " UTS_VERSION; +static bool kvm_para_has_feature(unsigned int feature) +{ + u32 kvm_base; + u32 features; + + if (!has_cpuflag(X86_FEATURE_HYPERVISOR)) + return false; + + kvm_base = hypervisor_cpuid_base("KVMKVMKVM\0\0\0", KVM_CPUID_FEATURES); + if (!kvm_base) + return false; + + features = cpuid_eax(kvm_base | KVM_CPUID_FEATURES); + return features & (1UL << feature); +} + #define I8254_PORT_CONTROL 0x43 #define I8254_PORT_COUNTER0 0x40 #define I8254_CMD_READBACK 0xC0 @@ -81,6 +99,15 @@ static unsigned long get_random_long(void) } } + if (kvm_para_has_feature(KVM_FEATURE_GET_RNG_SEED)) { + u64 seed; + + debug_putstr(" MSR_KVM_GET_RNG_SEED"); + rdmsrl(MSR_KVM_GET_RNG_SEED, seed); + random ^= (unsigned long)seed; + use_i8254 = false; + } + if (has_cpuflag(X86_FEATURE_TSC)) { debug_putstr(" RDTSC"); rdtscll(raw); -- 1.9.3 -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@...r.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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