forked from rpms/kernel
96 lines
3.5 KiB
Diff
96 lines
3.5 KiB
Diff
|
From 4758c1f8ad5385e53ea85739ad9f6fa6dfc0abda Mon Sep 17 00:00:00 2001
|
||
|
|
From: Nagappan Ramasamy Palaniappan <nagappan.ramasamy.palaniappan@oracle.com>
|
||
|
|
Date: Wed, 2 Aug 2023 12:55:46 +0000
|
||
|
|
Subject: [PATCH 3/5] x86/speculation: Allow enabling STIBP with legacy IBRS
|
||
|
|
MIME-Version: 1.0
|
||
|
|
Content-Type: text/plain; charset=UTF-8
|
||
|
|
Content-Transfer-Encoding: 8bit
|
||
|
|
|
||
|
|
When plain IBRS is enabled (not enhanced IBRS), the logic in
|
||
|
|
spectre_v2_user_select_mitigation() determines that STIBP is not needed.
|
||
|
|
|
||
|
|
The IBRS bit implicitly protects against cross-thread branch target
|
||
|
|
injection. However, with legacy IBRS, the IBRS bit is cleared on
|
||
|
|
returning to userspace for performance reasons which leaves userspace
|
||
|
|
threads vulnerable to cross-thread branch target injection against which
|
||
|
|
STIBP protects.
|
||
|
|
|
||
|
|
Exclude IBRS from the spectre_v2_in_ibrs_mode() check to allow for
|
||
|
|
enabling STIBP (through seccomp/prctl() by default or always-on, if
|
||
|
|
selected by spectre_v2_user kernel cmdline parameter).
|
||
|
|
|
||
|
|
[ bp: Massage. ]
|
||
|
|
|
||
|
|
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: KP Singh <kpsingh@kernel.org>
|
||
|
|
Signed-off-by: Borislav Petkov (AMD) <bp@alien8.de>
|
||
|
|
Signed-off-by: Nagappan Ramasamy Palaniappan <nagappan.ramasamy.palaniappan@oracle.com>
|
||
|
|
Reviewed-by: Laurence Rochfort <laurence.rochfort@oracle.com>
|
||
|
|
---
|
||
|
|
arch/x86/kernel/cpu/bugs.c | 25 ++++++++++++++++++-------
|
||
|
|
1 file changed, 18 insertions(+), 7 deletions(-)
|
||
|
|
|
||
|
|
diff --git a/arch/x86/kernel/cpu/bugs.c b/arch/x86/kernel/cpu/bugs.c
|
||
|
|
index da7c361f4..e13c4ecdc 100644
|
||
|
|
--- a/arch/x86/kernel/cpu/bugs.c
|
||
|
|
+++ b/arch/x86/kernel/cpu/bugs.c
|
||
|
|
@@ -1095,14 +1095,18 @@ 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)
|
||
|
|
{
|
||
|
|
@@ -1165,12 +1169,19 @@ spectre_v2_user_select_mitigation(void)
|
||
|
|
}
|
||
|
|
|
||
|
|
/*
|
||
|
|
- * If no STIBP, IBRS or enhanced IBRS is enabled, or SMT impossible,
|
||
|
|
- * STIBP is not required.
|
||
|
|
+ * If no STIBP, enhanced IBRS is enabled, or SMT impossible, STIBP
|
||
|
|
+ * is not required.
|
||
|
|
+ *
|
||
|
|
+ * Enhanced IBRS also protects against cross-thread branch target
|
||
|
|
+ * injection in user-mode as the IBRS bit remains always set which
|
||
|
|
+ * implicitly enables cross-thread protections. However, in legacy IBRS
|
||
|
|
+ * mode, the IBRS bit is set only on kernel entry and cleared on return
|
||
|
|
+ * to userspace. This disables the implicit cross-thread protection,
|
||
|
|
+ * so allow for STIBP to be selected in that case.
|
||
|
|
*/
|
||
|
|
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;
|
||
|
|
|
||
|
|
/*
|
||
|
|
@@ -2295,7 +2306,7 @@ static ssize_t mmio_stale_data_show_state(char *buf)
|
||
|
|
|
||
|
|
static char *stibp_state(void)
|
||
|
|
{
|
||
|
|
- if (spectre_v2_in_ibrs_mode(spectre_v2_enabled))
|
||
|
|
+ if (spectre_v2_in_eibrs_mode(spectre_v2_enabled))
|
||
|
|
return "";
|
||
|
|
|
||
|
|
switch (spectre_v2_user_stibp) {
|
||
|
|
--
|
||
|
|
2.31.1
|
||
|
|
|