diff options
| author | Thomas Gleixner <tglx@linutronix.de> | 2019-02-18 23:42:51 +0100 |
|---|---|---|
| committer | Thomas Gleixner <tglx@linutronix.de> | 2019-03-06 21:52:13 +0100 |
| commit | 04dcbdb8057827b043b3c71aa397c4c63e67d086 (patch) | |
| tree | ef837807f05eaf4ce6abe5d62b5ef5703931c3e5 /arch/x86/kernel | |
| parent | 6a9e529272517755904b7afa639f6db59ddb793e (diff) | |
x86/speculation/mds: Clear CPU buffers on exit to user
Add a static key which controls the invocation of the CPU buffer clear
mechanism on exit to user space and add the call into
prepare_exit_to_usermode() and do_nmi() right before actually returning.
Add documentation which kernel to user space transition this covers and
explain why some corner cases are not mitigated.
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Reviewed-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Reviewed-by: Borislav Petkov <bp@suse.de>
Reviewed-by: Frederic Weisbecker <frederic@kernel.org>
Reviewed-by: Jon Masters <jcm@redhat.com>
Tested-by: Jon Masters <jcm@redhat.com>
Diffstat (limited to 'arch/x86/kernel')
| -rw-r--r-- | arch/x86/kernel/cpu/bugs.c | 3 | ||||
| -rw-r--r-- | arch/x86/kernel/nmi.c | 4 | ||||
| -rw-r--r-- | arch/x86/kernel/traps.c | 8 |
3 files changed, 15 insertions, 0 deletions
diff --git a/arch/x86/kernel/cpu/bugs.c b/arch/x86/kernel/cpu/bugs.c index 01874d54f4fd..dbb45014de1b 100644 --- a/arch/x86/kernel/cpu/bugs.c +++ b/arch/x86/kernel/cpu/bugs.c @@ -63,6 +63,9 @@ DEFINE_STATIC_KEY_FALSE(switch_mm_cond_ibpb); /* Control unconditional IBPB in switch_mm() */ DEFINE_STATIC_KEY_FALSE(switch_mm_always_ibpb); +/* Control MDS CPU buffer clear before returning to user space */ +DEFINE_STATIC_KEY_FALSE(mds_user_clear); + void __init check_bugs(void) { identify_boot_cpu(); diff --git a/arch/x86/kernel/nmi.c b/arch/x86/kernel/nmi.c index 18bc9b51ac9b..086cf1d1d71d 100644 --- a/arch/x86/kernel/nmi.c +++ b/arch/x86/kernel/nmi.c @@ -34,6 +34,7 @@ #include <asm/x86_init.h> #include <asm/reboot.h> #include <asm/cache.h> +#include <asm/nospec-branch.h> #define CREATE_TRACE_POINTS #include <trace/events/nmi.h> @@ -533,6 +534,9 @@ nmi_restart: write_cr2(this_cpu_read(nmi_cr2)); if (this_cpu_dec_return(nmi_state)) goto nmi_restart; + + if (user_mode(regs)) + mds_user_clear_cpu_buffers(); } NOKPROBE_SYMBOL(do_nmi); diff --git a/arch/x86/kernel/traps.c b/arch/x86/kernel/traps.c index 9b7c4ca8f0a7..85fe1870f873 100644 --- a/arch/x86/kernel/traps.c +++ b/arch/x86/kernel/traps.c @@ -58,6 +58,7 @@ #include <asm/alternative.h> #include <asm/fpu/xstate.h> #include <asm/trace/mpx.h> +#include <asm/nospec-branch.h> #include <asm/mpx.h> #include <asm/vm86.h> #include <asm/umip.h> @@ -366,6 +367,13 @@ dotraplinkage void do_double_fault(struct pt_regs *regs, long error_code) regs->ip = (unsigned long)general_protection; regs->sp = (unsigned long)&gpregs->orig_ax; + /* + * This situation can be triggered by userspace via + * modify_ldt(2) and the return does not take the regular + * user space exit, so a CPU buffer clear is required when + * MDS mitigation is enabled. + */ + mds_user_clear_cpu_buffers(); return; } #endif |