[PATCH 4.19 04/18] x86/speculation: Add eIBRS + Retpoline options

Greg Kroah-Hartman
2022-03-09T16:09:18Z

From: Peter Zijlstra <peterz@infradead.org>

commit 1e19da8522c81bf46b335f84137165741e0d82b7 upstream.

Thanks to the chaps at VUsec it is now clear that eIBRS is not
sufficient, therefore allow enabling of retpolines along with eIBRS.

Add spectre_v2=eibrs, spectre_v2=eibrs,lfence and
spectre_v2=eibrs,retpoline options to explicitly pick your preferred
means of mitigation.

Since there's new mitigations there's also user visible changes in
/sys/devices/system/cpu/vulnerabilities/spectre_v2 to reflect these
new mitigations.

[ bp: Massage commit message, trim error messages,
do more precise eIBRS mode checking. ]

Co-developed-by: Josh Poimboeuf <jpoimboe@redhat.com>
Signed-off-by: Josh Poimboeuf <jpoimboe@redhat.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Signed-off-by: Borislav Petkov <bp@suse.de>
Reviewed-by: Patrick Colp <patrick.colp@oracle.com>
Reviewed-by: Thomas Gleixner <tglx@linutronix.de>
[fllinden@amazon.com: backported to 4.19 (no Hygon)]
Signed-off-by: Frank van der Linden <fllinden@amazon.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
---
arch/x86/include/asm/nospec-branch.h | 4 -
arch/x86/kernel/cpu/bugs.c | 131 +++++++++++++++++++++++++----------
2 files changed, 98 insertions(+), 37 deletions(-)

--- a/arch/x86/include/asm/nospec-branch.h
+++ b/arch/x86/include/asm/nospec-branch.h
@@ -225,7 +225,9 @@ enum spectre_v2_mitigation {
SPECTRE_V2_NONE,
SPECTRE_V2_RETPOLINE,
SPECTRE_V2_LFENCE,
- SPECTRE_V2_IBRS_ENHANCED,
+ SPECTRE_V2_EIBRS,
+ SPECTRE_V2_EIBRS_RETPOLINE,
+ SPECTRE_V2_EIBRS_LFENCE,
};

/* The indirect branch speculation control variants */
--- a/arch/x86/kernel/cpu/bugs.c
+++ b/arch/x86/kernel/cpu/bugs.c
@@ -622,6 +622,9 @@ enum spectre_v2_mitigation_cmd {
SPECTRE_V2_CMD_RETPOLINE,
SPECTRE_V2_CMD_RETPOLINE_GENERIC,
SPECTRE_V2_CMD_RETPOLINE_LFENCE,
+ SPECTRE_V2_CMD_EIBRS,
+ SPECTRE_V2_CMD_EIBRS_RETPOLINE,
+ SPECTRE_V2_CMD_EIBRS_LFENCE,
};

enum spectre_v2_user_cmd {
@@ -694,6 +697,13 @@ spectre_v2_parse_user_cmdline(enum spect
return SPECTRE_V2_USER_CMD_AUTO;
}

+static inline bool spectre_v2_in_eibrs_mode(enum spectre_v2_mitigation mode)
+{
+ return (mode == SPECTRE_V2_EIBRS ||
+ mode == SPECTRE_V2_EIBRS_RETPOLINE ||
+ mode == SPECTRE_V2_EIBRS_LFENCE);
+}
+
static void __init
spectre_v2_user_select_mitigation(enum spectre_v2_mitigation_cmd v2_cmd)
{
@@ -761,7 +771,7 @@ spectre_v2_user_select_mitigation(enum s
*/
if (!boot_cpu_has(X86_FEATURE_STIBP) ||
!smt_possible ||
- spectre_v2_enabled == SPECTRE_V2_IBRS_ENHANCED)
+ spectre_v2_in_eibrs_mode(spectre_v2_enabled))
return;

/*
@@ -783,7 +793,9 @@ static const char * const spectre_v2_str
[SPECTRE_V2_NONE] = "Vulnerable",
[SPECTRE_V2_RETPOLINE] = "Mitigation: Retpolines",
[SPECTRE_V2_LFENCE] = "Mitigation: LFENCE",
- [SPECTRE_V2_IBRS_ENHANCED] = "Mitigation: Enhanced IBRS",
+ [SPECTRE_V2_EIBRS] = "Mitigation: Enhanced IBRS",
+ [SPECTRE_V2_EIBRS_LFENCE] = "Mitigation: Enhanced IBRS + LFENCE",
+ [SPECTRE_V2_EIBRS_RETPOLINE] = "Mitigation: Enhanced IBRS + Retpolines",
};

static const struct {
@@ -797,6 +809,9 @@ static const struct {
{ "retpoline,amd", SPECTRE_V2_CMD_RETPOLINE_LFENCE, false },
{ "retpoline,lfence", SPECTRE_V2_CMD_RETPOLINE_LFENCE, false },
{ "retpoline,generic", SPECTRE_V2_CMD_RETPOLINE_GENERIC, false },
+ { "eibrs", SPECTRE_V2_CMD_EIBRS, false },
+ { "eibrs,lfence", SPECTRE_V2_CMD_EIBRS_LFENCE, false },
+ { "eibrs,retpoline", SPECTRE_V2_CMD_EIBRS_RETPOLINE, false },
{ "auto", SPECTRE_V2_CMD_AUTO, false },
};

@@ -834,15 +849,29 @@ static enum spectre_v2_mitigation_cmd __

if ((cmd == SPECTRE_V2_CMD_RETPOLINE ||
cmd == SPECTRE_V2_CMD_RETPOLINE_LFENCE ||
- cmd == SPECTRE_V2_CMD_RETPOLINE_GENERIC) &&
+ cmd == SPECTRE_V2_CMD_RETPOLINE_GENERIC ||
+ cmd == SPECTRE_V2_CMD_EIBRS_LFENCE ||
+ cmd == SPECTRE_V2_CMD_EIBRS_RETPOLINE) &&
!IS_ENABLED(CONFIG_RETPOLINE)) {
- pr_err("%s selected but not compiled in. Switching to AUTO select\n", mitigation_options[i].option);
+ pr_err("%s selected but not compiled in. Switching to AUTO select\n",
+ mitigation_options[i].option);
+ return SPECTRE_V2_CMD_AUTO;
+ }
+
+ if ((cmd == SPECTRE_V2_CMD_EIBRS ||
+ cmd == SPECTRE_V2_CMD_EIBRS_LFENCE ||
+ cmd == SPECTRE_V2_CMD_EIBRS_RETPOLINE) &&
+ !boot_cpu_has(X86_FEATURE_IBRS_ENHANCED)) {
+ pr_err("%s selected but CPU doesn't have eIBRS. Switching to AUTO select\n",
+ mitigation_options[i].option);
return SPECTRE_V2_CMD_AUTO;
}

- if ((cmd == SPECTRE_V2_CMD_RETPOLINE_LFENCE) &&
+ if ((cmd == SPECTRE_V2_CMD_RETPOLINE_LFENCE ||
+ cmd == SPECTRE_V2_CMD_EIBRS_LFENCE) &&
!boot_cpu_has(X86_FEATURE_LFENCE_RDTSC)) {
- pr_err("%s selected, but CPU doesn't have a serializing LFENCE. Switching to AUTO select\n", mitigation_options[i].option);
+ pr_err("%s selected, but CPU doesn't have a serializing LFENCE. Switching to AUTO select\n",
+ mitigation_options[i].option);
return SPECTRE_V2_CMD_AUTO;
}

@@ -851,6 +880,24 @@ static enum spectre_v2_mitigation_cmd __
return cmd;
}

+static enum spectre_v2_mitigation __init spectre_v2_select_retpoline(void)
+{
+ if (!IS_ENABLED(CONFIG_RETPOLINE)) {
+ pr_err("Kernel not compiled with retpoline; no mitigation available!");
+ return SPECTRE_V2_NONE;
+ }
+
+ if (boot_cpu_data.x86_vendor == X86_VENDOR_AMD) {
+ if (!boot_cpu_has(X86_FEATURE_LFENCE_RDTSC)) {
+ pr_err("LFENCE not serializing, switching to generic retpoline\n");
+ return SPECTRE_V2_RETPOLINE;
+ }
+ return SPECTRE_V2_LFENCE;
+ }
+
+ return SPECTRE_V2_RETPOLINE;
+}
+
static void __init spectre_v2_select_mitigation(void)
{
enum spectre_v2_mitigation_cmd cmd = spectre_v2_parse_cmdline();
@@ -871,48 +918,60 @@ static void __init spectre_v2_select_mit
case SPECTRE_V2_CMD_FORCE:
case SPECTRE_V2_CMD_AUTO:
if (boot_cpu_has(X86_FEATURE_IBRS_ENHANCED)) {
- mode = SPECTRE_V2_IBRS_ENHANCED;
- /* Force it so VMEXIT will restore correctly */
- x86_spec_ctrl_base |= SPEC_CTRL_IBRS;
- wrmsrl(MSR_IA32_SPEC_CTRL, x86_spec_ctrl_base);
- goto specv2_set_mode;
+ mode = SPECTRE_V2_EIBRS;
+ break;
}
- if (IS_ENABLED(CONFIG_RETPOLINE))
- goto retpoline_auto;
+
+ mode = spectre_v2_select_retpoline();
break;
+
case SPECTRE_V2_CMD_RETPOLINE_LFENCE:
- if (IS_ENABLED(CONFIG_RETPOLINE))
- goto retpoline_lfence;
+ mode = SPECTRE_V2_LFENCE;
break;
+
case SPECTRE_V2_CMD_RETPOLINE_GENERIC:
- if (IS_ENABLED(CONFIG_RETPOLINE))
- goto retpoline_generic;
+ mode = SPECTRE_V2_RETPOLINE;
break;
+
case SPECTRE_V2_CMD_RETPOLINE:
- if (IS_ENABLED(CONFIG_RETPOLINE))
- goto retpoline_auto;
+ mode = spectre_v2_select_retpoline();
+ break;
+
+ case SPECTRE_V2_CMD_EIBRS:
+ mode = SPECTRE_V2_EIBRS;
+ break;
+
+ case SPECTRE_V2_CMD_EIBRS_LFENCE:
+ mode = SPECTRE_V2_EIBRS_LFENCE;
+ break;
+
+ case SPECTRE_V2_CMD_EIBRS_RETPOLINE:
+ mode = SPECTRE_V2_EIBRS_RETPOLINE;
break;
}
- pr_err("Spectre mitigation: kernel not compiled with retpoline; no mitigation available!");
- return;

-retpoline_auto:
- if (boot_cpu_data.x86_vendor == X86_VENDOR_AMD) {
- retpoline_lfence:
- if (!boot_cpu_has(X86_FEATURE_LFENCE_RDTSC)) {
- pr_err("Spectre mitigation: LFENCE not serializing, switching to generic retpoline\n");
- goto retpoline_generic;
- }
- mode = SPECTRE_V2_LFENCE;
+ if (spectre_v2_in_eibrs_mode(mode)) {
+ /* Force it so VMEXIT will restore correctly */
+ x86_spec_ctrl_base |= SPEC_CTRL_IBRS;
+ wrmsrl(MSR_IA32_SPEC_CTRL, x86_spec_ctrl_base);
+ }
+
+ switch (mode) {
+ case SPECTRE_V2_NONE:
+ case SPECTRE_V2_EIBRS:
+ break;
+
+ case SPECTRE_V2_LFENCE:
+ case SPECTRE_V2_EIBRS_LFENCE:
setup_force_cpu_cap(X86_FEATURE_RETPOLINE_LFENCE);
+ /* fallthrough */
+
+ case SPECTRE_V2_RETPOLINE:
+ case SPECTRE_V2_EIBRS_RETPOLINE:
setup_force_cpu_cap(X86_FEATURE_RETPOLINE);
- } else {
- retpoline_generic:
- mode = SPECTRE_V2_RETPOLINE;
- setup_force_cpu_cap(X86_FEATURE_RETPOLINE);
+ break;
}

-specv2_set_mode:
spectre_v2_enabled = mode;
pr_info("%s\n", spectre_v2_strings[mode]);

@@ -938,7 +997,7 @@ specv2_set_mode:
* the CPU supports Enhanced IBRS, kernel might un-intentionally not
* enable IBRS around firmware calls.
*/
- if (boot_cpu_has(X86_FEATURE_IBRS) && mode != SPECTRE_V2_IBRS_ENHANCED) {
+ if (boot_cpu_has(X86_FEATURE_IBRS) && !spectre_v2_in_eibrs_mode(mode)) {
setup_force_cpu_cap(X86_FEATURE_USE_IBRS_FW);
pr_info("Enabling Restricted Speculation for firmware calls\n");
}
@@ -1596,7 +1655,7 @@ static ssize_t tsx_async_abort_show_stat

static char *stibp_state(void)
{
- if (spectre_v2_enabled == SPECTRE_V2_IBRS_ENHANCED)
+ if (spectre_v2_in_eibrs_mode(spectre_v2_enabled))
return "";

switch (spectre_v2_user_stibp) {