Messages in this thread Patch in this message |  | | Date | Sun, 11 Feb 2018 19:50:57 +0100 | From | Ingo Molnar <> | Subject | [PATCH] x86/speculation: Clean up various Spectre related details |
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* David Woodhouse <dwmw@amazon.co.uk> wrote:
> + /* > + * Retpoline means the kernel is safe because it has no indirect > + * branches. But firmware isn't, so use IBRS to protect that. > + */ > + if (boot_cpu_has(X86_FEATURE_IBRS)) { > + setup_force_cpu_cap(X86_FEATURE_USE_IBRS_FW); > + pr_info("Enabling Restricted Speculation for firmware calls\n"); > + }
I have changed this text to say:
pr_info("Spectre mitigation: Restricting branch speculation (enabling IBRS) for firmware calls\n");
In fact while at it I found and improved a few other details as well, such as:
* Retpoline means the kernel is safe because it has no indirect - * branches. But firmware isn't, so use IBRS to protect that. + * branches. But we don't know whether the firmware is safe, so + * use IBRS to protect against that:
most Spectre related messages are now harmonized:
arch/x86/kernel/cpu/bugs.c: pr_info("Spectre mitigation: Filling RSB on context switch\n"); arch/x86/kernel/cpu/bugs.c: pr_info("Spectre mitigation: Enabling Indirect Branch Prediction Barrier (IBPB)\n"); arch/x86/kernel/cpu/bugs.c: pr_info("Spectre mitigation: Restricting branch speculation (enabling IBRS) for firmware calls\n");
Find the full patch below.
Thanks,
Ingo
=========================> From 82c2b2f29691143a05181333f387e786646aa28b Mon Sep 17 00:00:00 2001 From: Ingo Molnar <mingo@kernel.org> Date: Sat, 10 Feb 2018 11:51:57 +0100 Subject: [PATCH] x86/speculation: Clean up various Spectre related details
Harmonize all the Spectre messages so that a:
dmesg | grep -i spectre
... gives us most Spectre related kernel boot messages.
Also fix a few other details:
- clarify a comment about firmware speculation control
- s/KPTI/PTI
- remove various line-breaks that made the code uglier
Cc: Andy Lutomirski <luto@kernel.org> Cc: Arjan van de Ven <arjan@linux.intel.com> Cc: Borislav Petkov <bp@alien8.de> Cc: Dan Williams <dan.j.williams@intel.com> Cc: Dave Hansen <dave.hansen@linux.intel.com> Cc: David Woodhouse <dwmw2@infradead.org> Cc: David Woodhouse <dwmw@amazon.co.uk> Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org> Cc: Josh Poimboeuf <jpoimboe@redhat.com> Cc: Linus Torvalds <torvalds@linux-foundation.org> Cc: Peter Zijlstra <peterz@infradead.org> Cc: Thomas Gleixner <tglx@linutronix.de> Signed-off-by: Ingo Molnar <mingo@kernel.org> --- arch/x86/kernel/cpu/bugs.c | 33 ++++++++++++++------------------- 1 file changed, 14 insertions(+), 19 deletions(-)
diff --git a/arch/x86/kernel/cpu/bugs.c b/arch/x86/kernel/cpu/bugs.c index 6f6d763225c8..eff45477fcca 100644 --- a/arch/x86/kernel/cpu/bugs.c +++ b/arch/x86/kernel/cpu/bugs.c @@ -162,8 +162,7 @@ static enum spectre_v2_mitigation_cmd __init spectre_v2_parse_cmdline(void) if (cmdline_find_option_bool(boot_command_line, "nospectre_v2")) return SPECTRE_V2_CMD_NONE; else { - ret = cmdline_find_option(boot_command_line, "spectre_v2", arg, - sizeof(arg)); + ret = cmdline_find_option(boot_command_line, "spectre_v2", arg, sizeof(arg)); if (ret < 0) return SPECTRE_V2_CMD_AUTO; @@ -175,8 +174,7 @@ static enum spectre_v2_mitigation_cmd __init spectre_v2_parse_cmdline(void) } if (i >= ARRAY_SIZE(mitigation_options)) { - pr_err("unknown option (%s). Switching to AUTO select\n", - mitigation_options[i].option); + pr_err("unknown option (%s). Switching to AUTO select\n", mitigation_options[i].option); return SPECTRE_V2_CMD_AUTO; } } @@ -185,8 +183,7 @@ static enum spectre_v2_mitigation_cmd __init spectre_v2_parse_cmdline(void) cmd == SPECTRE_V2_CMD_RETPOLINE_AMD || cmd == SPECTRE_V2_CMD_RETPOLINE_GENERIC) && !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; } @@ -256,14 +253,14 @@ static void __init spectre_v2_select_mitigation(void) goto retpoline_auto; break; } - pr_err("kernel not compiled with retpoline; no mitigation available!"); + 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_amd: if (!boot_cpu_has(X86_FEATURE_LFENCE_RDTSC)) { - pr_err("LFENCE not serializing. Switching to generic retpoline\n"); + pr_err("Spectre mitigation: LFENCE not serializing, switching to generic retpoline\n"); goto retpoline_generic; } mode = retp_compiler() ? SPECTRE_V2_RETPOLINE_AMD : @@ -281,7 +278,7 @@ static void __init spectre_v2_select_mitigation(void) pr_info("%s\n", spectre_v2_strings[mode]); /* - * If neither SMEP or KPTI are available, there is a risk of + * If neither SMEP or PTI are available, there is a risk of * hitting userspace addresses in the RSB after a context switch * from a shallow call stack to a deeper one. To prevent this fill * the entire RSB, even when using IBRS. @@ -295,30 +292,30 @@ static void __init spectre_v2_select_mitigation(void) if ((!boot_cpu_has(X86_FEATURE_PTI) && !boot_cpu_has(X86_FEATURE_SMEP)) || is_skylake_era()) { setup_force_cpu_cap(X86_FEATURE_RSB_CTXSW); - pr_info("Filling RSB on context switch\n"); + pr_info("Spectre mitigation: Filling RSB on context switch\n"); } /* Initialize Indirect Branch Prediction Barrier if supported */ if (boot_cpu_has(X86_FEATURE_IBPB)) { setup_force_cpu_cap(X86_FEATURE_USE_IBPB); - pr_info("Enabling Indirect Branch Prediction Barrier\n"); + pr_info("Spectre mitigation: Enabling Indirect Branch Prediction Barrier (IBPB)\n"); } /* * Retpoline means the kernel is safe because it has no indirect - * branches. But firmware isn't, so use IBRS to protect that. + * branches. But we don't know whether the firmware is safe, so + * use IBRS to protect against that: */ if (boot_cpu_has(X86_FEATURE_IBRS)) { setup_force_cpu_cap(X86_FEATURE_USE_IBRS_FW); - pr_info("Enabling Restricted Speculation for firmware calls\n"); + pr_info("Spectre mitigation: Restricting branch speculation (enabling IBRS) for firmware calls\n"); } } #undef pr_fmt #ifdef CONFIG_SYSFS -ssize_t cpu_show_meltdown(struct device *dev, - struct device_attribute *attr, char *buf) +ssize_t cpu_show_meltdown(struct device *dev, struct device_attribute *attr, char *buf) { if (!boot_cpu_has_bug(X86_BUG_CPU_MELTDOWN)) return sprintf(buf, "Not affected\n"); @@ -327,16 +324,14 @@ ssize_t cpu_show_meltdown(struct device *dev, return sprintf(buf, "Vulnerable\n"); } -ssize_t cpu_show_spectre_v1(struct device *dev, - struct device_attribute *attr, char *buf) +ssize_t cpu_show_spectre_v1(struct device *dev, struct device_attribute *attr, char *buf) { if (!boot_cpu_has_bug(X86_BUG_SPECTRE_V1)) return sprintf(buf, "Not affected\n"); return sprintf(buf, "Mitigation: __user pointer sanitization\n"); } -ssize_t cpu_show_spectre_v2(struct device *dev, - struct device_attribute *attr, char *buf) +ssize_t cpu_show_spectre_v2(struct device *dev, struct device_attribute *attr, char *buf) { if (!boot_cpu_has_bug(X86_BUG_SPECTRE_V2)) return sprintf(buf, "Not affected\n");
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