x86/speculation: STUFF_RSB dynamic enable

The STUFF_RSB overwrite macro can be enabled dynamically with
rsb_overwrite_key instead of using X86_FEATURE_STUFF_RSB.

Signed-off-by: William Roche <william.roche@oracle.com>
Co-developed-by: Alexandre Chartre <alexandre.chartre@oracle.com>
Signed-off-by: Alexandre Chartre <alexandre.chartre@oracle.com>
Reviewed-by: Darren Kenny <darren.kenny@oracle.com>
Reviewed-by: Boris Ostrovsky <boris.ostrovsky@oracle.com>
Reviewed-by: Alejandro Jimenez <alejandro.j.jimenez@oracle.com>
(cherry picked from commit 84e09871beb92364bd374d8c3bc3441a8c4be593)

Orabug: 29660924

Signed-off-by: William Roche <william.roche@oracle.com>
Reviewed-by: Darren Kenny <darren.kenny@oracle.com>
Acked-by: Boris Ostrovsky <boris.ostrovsky@oracle.com>
Signed-off-by: Brian Maly <brian.maly@oracle.com>
Conflicts:
	arch/x86/include/asm/cpufeatures.h
	arch/x86/include/asm/spec_ctrl.h
	arch/x86/kernel/cpu/bugs.c
cpufeatures.h vs cpufeature.h in UEK4
include <linux/jump_label.h> header in spec_ctrl.h to use this feature
bugs.c vs bugs_64.c in UEK4

Signed-off-by: Brian Maly <brian.maly@oracle.com>

diff --git a/arch/x86/include/asm/cpufeature.h b/arch/x86/include/asm/cpufeature.h
index 6455f591257d09594a2e9183283702279fe5d8bd..fba248660005698f103b3f780baca9885b560096 100644 (file)
--- a/arch/x86/include/asm/cpufeature.h
+++ b/arch/x86/include/asm/cpufeature.h
@@ -216,7 +216,6 @@
 #define X86_FEATURE_SSBD               ( 7*32+25) /* Speculative Store Bypass Disable */
 #define X86_FEATURE_SPEC_STORE_BYPASS_DISABLE ( 7*32+26) /* "" Disable Speculative Store Bypass. */
 #define X86_FEATURE_VMEXIT_RSB_FULL    (7*32+27) /* "" Whether to stuff the RSB on VMEXIT. */
-#define X86_FEATURE_STUFF_RSB  (7*32+28) /* "" Whether to stuff the RSB (usually dependent on !SMEP) */
 #define X86_FEATURE_RETPOLINE  ( 7*32+29) /* "" Generic Retpoline mitigation for Spectre variant 2 */
 #define X86_FEATURE_RETPOLINE_AMD ( 7*32+30) /* "" AMD Retpoline mitigation for Spectre variant 2 */
 /* Because the ALTERNATIVE scheme is for members of the X86_FEATURE club... */

diff --git a/arch/x86/include/asm/spec_ctrl.h b/arch/x86/include/asm/spec_ctrl.h
index 09e8b761a74dbedf8325802dde0a9adc0d905d41..48877d6857bc60d6edc44fc088115f6563f172a9 100644 (file)
--- a/arch/x86/include/asm/spec_ctrl.h
+++ b/arch/x86/include/asm/spec_ctrl.h
@@ -1,6 +1,7 @@
 #ifndef _ASM_X86_SPEC_CTRL_H
 #define _ASM_X86_SPEC_CTRL_H
 
+#include <linux/jump_label.h>
 #include <linux/stringify.h>
 #include <asm/msr-index.h>
 #include <asm/cpufeature.h>
@@ -187,8 +188,15 @@
 9:
 .endm
 
+/*
+ * Overwrite RSB stuffing macro.
+ */
 .macro STUFF_RSB
-ALTERNATIVE __stringify(__ASM_STUFF_RSB), "", X86_FEATURE_STUFF_RSB
+       STATIC_JUMP_IF_TRUE .Lstuff_rsb_\@, rsb_overwrite_key, def=0
+       jmp     .Ldone_call_\@
+.Lstuff_rsb_\@:
+       __ASM_STUFF_RSB
+.Ldone_call_\@:
 .endm
 
 #else /* __ASSEMBLY__ */
@@ -219,6 +227,17 @@ extern void unprotected_firmware_begin(void);
 extern void unprotected_firmware_end(void);
 
 DECLARE_STATIC_KEY_FALSE(retpoline_enabled_key);
+DECLARE_STATIC_KEY_FALSE(rsb_overwrite_key);
+
+static inline void rsb_overwrite_enable(void)
+{
+       static_branch_enable(&rsb_overwrite_key);
+}
+
+static inline void rsb_overwrite_disable(void)
+{
+       static_branch_disable(&rsb_overwrite_key);
+}
 
 #define ibrs_firmware          (use_ibrs & SPEC_CTRL_IBRS_FIRMWARE)
 #define ibrs_supported         (use_ibrs & SPEC_CTRL_IBRS_SUPPORTED)

diff --git a/arch/x86/kernel/cpu/bugs_64.c b/arch/x86/kernel/cpu/bugs_64.c
index 58ff9433927dc66b59cba9fc38ff35d7942a99f5..5c27c37ee36b9696813893be77c5bd4fc67b232c 100644 (file)
--- a/arch/x86/kernel/cpu/bugs_64.c
+++ b/arch/x86/kernel/cpu/bugs_64.c
@@ -76,6 +76,12 @@ static enum spectre_v2_mitigation retpoline_mode = SPECTRE_V2_NONE;
 DEFINE_STATIC_KEY_FALSE(retpoline_enabled_key);
 EXPORT_SYMBOL(retpoline_enabled_key);
 
+/*
+ * RSB stuffing dynamic key to activate the STUFF_RSB overwrite macro.
+ */
+DEFINE_STATIC_KEY_FALSE(rsb_overwrite_key);
+EXPORT_SYMBOL(rsb_overwrite_key);
+
 static bool is_skylake_era(void);
 static void disable_ibrs_and_friends(bool);
 static void activate_spectre_v2_mitigation(enum spectre_v2_mitigation);
@@ -700,7 +706,8 @@ static void ibrs_select(enum spectre_v2_mitigation *mode)
        if (boot_cpu_has(X86_FEATURE_SMEP))
                return;
 
-       setup_force_cpu_cap(X86_FEATURE_STUFF_RSB);
+       /* IBRS without SMEP needs RSB overwrite */
+       rsb_overwrite_enable();
 
        if (*mode == SPECTRE_V2_IBRS_ENHANCED)
                pr_warn("Enhanced IBRS might not provide full mitigation against Spectre v2 if SMEP is not available.\n");