Messages in this thread Patch in this message | | | Date | Tue, 2 Apr 2024 22:54:19 -0700 | From | Pawan Gupta <> | Subject | [PATCH v3] x86/bugs: Default retbleed to =stuff when retpoline is enabled |
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On Intel systems when retpoline mitigation is enabled for spectre-v2, retbleed=auto does not enable RSB stuffing. This may make the system vulnerable to retbleed. Retpoline is not the default mitigation when IBRS is present, but in virtualized cases a VMM can hide IBRS from guests, resulting in guest deploying retpoline by default. Even if IBRS is enumerated, a user can still select spectre_v2=retpoline.
As with other mitigations, mitigate retbleed by default. On Intel systems when retpoline is enabled, and retbleed mitigation is set to auto, enable Call Depth Tracking and RSB stuffing i.e. retbleed=stuff mitigation. For AMD/Hygon auto mode already selects the appropriate mitigation.
Reported-by: Alyssa Milburn <alyssa.milburn@intel.com> Cc: stable@kernel.org Signed-off-by: Pawan Gupta <pawan.kumar.gupta@linux.intel.com> --- v3: - Rebased to v6.9-rc2
v2: https://lore.kernel.org/r/20240212-retbleed-auto-stuff-v2-1-89401649341a@linux.intel.com - Mitigate retbleed by default for spectre_v2=retpoline. (Josh) - Add the missing ',' in the comment. (Josh) - Rebased to v6.8-rc4
v1: https://lore.kernel.org/r/20240208-retbleed-auto-stuff-v1-1-6f12e513868f@linux.intel.com --- arch/x86/kernel/cpu/bugs.c | 10 ++++++++-- 1 file changed, 8 insertions(+), 2 deletions(-)
diff --git a/arch/x86/kernel/cpu/bugs.c b/arch/x86/kernel/cpu/bugs.c index e7ba936d798b..69d8ce58f244 100644 --- a/arch/x86/kernel/cpu/bugs.c +++ b/arch/x86/kernel/cpu/bugs.c @@ -1092,11 +1092,17 @@ static void __init retbleed_select_mitigation(void) else if (IS_ENABLED(CONFIG_MITIGATION_IBPB_ENTRY) && boot_cpu_has(X86_FEATURE_IBPB)) retbleed_mitigation = RETBLEED_MITIGATION_IBPB; + } else if (boot_cpu_data.x86_vendor == X86_VENDOR_INTEL && + spectre_v2_enabled == SPECTRE_V2_RETPOLINE) { + if (IS_ENABLED(CONFIG_CALL_DEPTH_TRACKING)) + retbleed_mitigation = RETBLEED_MITIGATION_STUFF; + else + pr_err("WARNING: Retpoline enabled, but kernel not compiled with CALL_DEPTH_TRACKING.\n"); } /* - * The Intel mitigation (IBRS or eIBRS) was already selected in - * spectre_v2_select_mitigation(). 'retbleed_mitigation' will + * If Intel mitigation (IBRS or eIBRS) was already selected in + * spectre_v2_select_mitigation(), 'retbleed_mitigation' will * be set accordingly below. */ --- base-commit: 39cd87c4eb2b893354f3b850f916353f2658ae6f change-id: 20240208-retbleed-auto-stuff-53e0fa91305e
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