From c2955f270a84762343000f103e0640d29c7a96f3 Mon Sep 17 00:00:00 2001 From: Pawan Gupta Date: Wed, 23 Oct 2019 10:45:50 +0200 Subject: [PATCH] x86/msr: Add the IA32_TSX_CTRL MSR Transactional Synchronization Extensions (TSX) may be used on certain processors as part of a speculative side channel attack. A microcode update for existing processors that are vulnerable to this attack will add a new MSR - IA32_TSX_CTRL to allow the system administrator the option to disable TSX as one of the possible mitigations. The CPUs which get this new MSR after a microcode upgrade are the ones which do not set MSR_IA32_ARCH_CAPABILITIES.MDS_NO (bit 5) because those CPUs have CPUID.MD_CLEAR, i.e., the VERW implementation which clears all CPU buffers takes care of the TAA case as well. [ Note that future processors that are not vulnerable will also support the IA32_TSX_CTRL MSR. ] Add defines for the new IA32_TSX_CTRL MSR and its bits. TSX has two sub-features: 1. Restricted Transactional Memory (RTM) is an explicitly-used feature where new instructions begin and end TSX transactions. 2. Hardware Lock Elision (HLE) is implicitly used when certain kinds of "old" style locks are used by software. Bit 7 of the IA32_ARCH_CAPABILITIES indicates the presence of the IA32_TSX_CTRL MSR. There are two control bits in IA32_TSX_CTRL MSR: Bit 0: When set, it disables the Restricted Transactional Memory (RTM) sub-feature of TSX (will force all transactions to abort on the XBEGIN instruction). Bit 1: When set, it disables the enumeration of the RTM and HLE feature (i.e. it will make CPUID(EAX=7).EBX{bit4} and CPUID(EAX=7).EBX{bit11} read as 0). The other TSX sub-feature, Hardware Lock Elision (HLE), is unconditionally disabled by the new microcode but still enumerated as present by CPUID(EAX=7).EBX{bit4}, unless disabled by IA32_TSX_CTRL_MSR[1] - TSX_CTRL_CPUID_CLEAR. Signed-off-by: Pawan Gupta Signed-off-by: Borislav Petkov Signed-off-by: Thomas Gleixner Tested-by: Neelima Krishnan Reviewed-by: Mark Gross Reviewed-by: Tony Luck Reviewed-by: Josh Poimboeuf --- arch/x86/include/asm/msr-index.h | 5 +++++ 1 file changed, 5 insertions(+) diff --git a/arch/x86/include/asm/msr-index.h b/arch/x86/include/asm/msr-index.h index 20ce682a2540..da4caf6da739 100644 --- a/arch/x86/include/asm/msr-index.h +++ b/arch/x86/include/asm/msr-index.h @@ -93,6 +93,7 @@ * Microarchitectural Data * Sampling (MDS) vulnerabilities. */ +#define ARCH_CAP_TSX_CTRL_MSR BIT(7) /* MSR for TSX control is available. */ #define MSR_IA32_FLUSH_CMD 0x0000010b #define L1D_FLUSH BIT(0) /* @@ -103,6 +104,10 @@ #define MSR_IA32_BBL_CR_CTL 0x00000119 #define MSR_IA32_BBL_CR_CTL3 0x0000011e +#define MSR_IA32_TSX_CTRL 0x00000122 +#define TSX_CTRL_RTM_DISABLE BIT(0) /* Disable RTM feature */ +#define TSX_CTRL_CPUID_CLEAR BIT(1) /* Disable TSX enumeration */ + #define MSR_IA32_SYSENTER_CS 0x00000174 #define MSR_IA32_SYSENTER_ESP 0x00000175 #define MSR_IA32_SYSENTER_EIP 0x00000176 -- GitLab