IBRS is only enabled in kernel space. Since it's not enabled in user space, user space isn't protected from indirect branch prediction attacks from a sibling CPU thread.
Allow STIBP to be enabled to protect against such attacks.
Fixes: 7c693f54c873 ("x86/speculation: Add spectre_v2=ibrs option to support Kernel IBRS") Reported-by: José Oliveira joseloliveira11@gmail.com Reported-by: Rodrigo Branco rodrigo@kernelhacking.com Signed-off-by: Josh Poimboeuf jpoimboe@kernel.org --- arch/x86/kernel/cpu/bugs.c | 18 ++++++++++-------- 1 file changed, 10 insertions(+), 8 deletions(-)
diff --git a/arch/x86/kernel/cpu/bugs.c b/arch/x86/kernel/cpu/bugs.c index 85168740f76a..b97c0d28e573 100644 --- a/arch/x86/kernel/cpu/bugs.c +++ b/arch/x86/kernel/cpu/bugs.c @@ -1124,14 +1124,19 @@ spectre_v2_parse_user_cmdline(void) return SPECTRE_V2_USER_CMD_AUTO; }
-static inline bool spectre_v2_in_ibrs_mode(enum spectre_v2_mitigation mode) +static inline bool spectre_v2_in_eibrs_mode(enum spectre_v2_mitigation mode) { - return mode == SPECTRE_V2_IBRS || - mode == SPECTRE_V2_EIBRS || + return mode == SPECTRE_V2_EIBRS || mode == SPECTRE_V2_EIBRS_RETPOLINE || mode == SPECTRE_V2_EIBRS_LFENCE; }
+static inline bool spectre_v2_in_ibrs_mode(enum spectre_v2_mitigation mode) +{ + return spectre_v2_in_eibrs_mode(mode) || + mode == SPECTRE_V2_IBRS; +} + static void __init spectre_v2_user_select_mitigation(void) { @@ -1194,12 +1199,12 @@ spectre_v2_user_select_mitigation(void) }
/* - * If no STIBP, IBRS or enhanced IBRS is enabled, or SMT impossible, + * If no STIBP, enhanced IBRS is enabled, or SMT impossible, * STIBP is not required. */ if (!boot_cpu_has(X86_FEATURE_STIBP) || !smt_possible || - spectre_v2_in_ibrs_mode(spectre_v2_enabled)) + spectre_v2_in_eibrs_mode(spectre_v2_enabled)) return;
/* @@ -2327,9 +2332,6 @@ static ssize_t mmio_stale_data_show_state(char *buf)
static char *stibp_state(void) { - if (spectre_v2_in_ibrs_mode(spectre_v2_enabled)) - return ""; - switch (spectre_v2_user_stibp) { case SPECTRE_V2_USER_NONE: return ", STIBP: disabled";