From mboxrd@z Thu Jan 1 00:00:00 1970 From: Kristen Carlson Accardi Subject: [RFC PATCH] x86: entry: flush the cache if syscall error Date: Mon, 10 Sep 2018 12:10:02 -0700 Message-Id: <20180910191002.350195-1-kristen@linux.intel.com> To: kernel-hardening@lists.openwall.com List-ID: This patch aims to make it harder to perform cache timing attacks on data left behind by system calls. If we have an error returned from a syscall, flush the L1 cache. Signed-off-by: Kristen Carlson Accardi --- arch/x86/Kconfig | 8 ++++++++ arch/x86/entry/common.c | 20 ++++++++++++++++++++ 2 files changed, 28 insertions(+) diff --git a/arch/x86/Kconfig b/arch/x86/Kconfig index c5ff296bc5d1..8a67642ff9fe 100644 --- a/arch/x86/Kconfig +++ b/arch/x86/Kconfig @@ -445,6 +445,14 @@ config RETPOLINE code are eliminated. Since this includes the syscall entry path, it is not entirely pointless. +config SYSCALL_FLUSH + bool "Clear L1 Cache on syscall errors" + default y + help + Select to allow the L1 cache to be cleared upon return of + an error code from a syscall. This will reduce the likelyhood of + speculative execution style attacks on syscalls. + config INTEL_RDT bool "Intel Resource Director Technology support" default n diff --git a/arch/x86/entry/common.c b/arch/x86/entry/common.c index 3b2490b81918..77beff541013 100644 --- a/arch/x86/entry/common.c +++ b/arch/x86/entry/common.c @@ -268,6 +268,22 @@ __visible inline void syscall_return_slowpath(struct pt_regs *regs) prepare_exit_to_usermode(regs); } +__visible inline void l1_cache_flush(struct pt_regs *regs) +{ + if (IS_ENABLED(CONFIG_SYSCALL_FLUSH)) { + if (regs->ax == 0 || regs->ax == -EAGAIN || + regs->ax == -EEXIST || regs->ax == -ENOENT || + regs->ax == -EXDEV || regs->ax == -ETIMEDOUT || + regs->ax == -ENOTCONN || regs->ax == -EINPROGRESS) + return; + + if (static_cpu_has(X86_FEATURE_FLUSH_L1D)) { + wrmsrl(MSR_IA32_FLUSH_CMD, L1D_FLUSH); + return; + } + } +} + #ifdef CONFIG_X86_64 __visible void do_syscall_64(unsigned long nr, struct pt_regs *regs) { @@ -290,6 +306,8 @@ __visible void do_syscall_64(unsigned long nr, struct pt_regs *regs) regs->ax = sys_call_table[nr](regs); } + l1_cache_flush(regs); + syscall_return_slowpath(regs); } #endif @@ -338,6 +356,8 @@ static __always_inline void do_syscall_32_irqs_on(struct pt_regs *regs) #endif /* CONFIG_IA32_EMULATION */ } + l1_cache_flush(regs); + syscall_return_slowpath(regs); } -- 2.14.4