133 lines
4.5 KiB
Diff
133 lines
4.5 KiB
Diff
From: Michal Hocko <mhocko@suse.com>
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Date: Wed, 23 Oct 2019 12:35:50 +0200
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Subject: x86/tsx: Add config options to set tsx=on|off|auto
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commit db616173d787395787ecc93eef075fa975227b10 upstream.
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There is a general consensus that TSX usage is not largely spread while
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the history shows there is a non trivial space for side channel attacks
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possible. Therefore the tsx is disabled by default even on platforms
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that might have a safe implementation of TSX according to the current
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knowledge. This is a fair trade off to make.
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There are, however, workloads that really do benefit from using TSX and
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updating to a newer kernel with TSX disabled might introduce a
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noticeable regressions. This would be especially a problem for Linux
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distributions which will provide TAA mitigations.
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Introduce config options X86_INTEL_TSX_MODE_OFF, X86_INTEL_TSX_MODE_ON
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and X86_INTEL_TSX_MODE_AUTO to control the TSX feature. The config
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setting can be overridden by the tsx cmdline options.
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[ bp: Text cleanups from Josh. ]
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Suggested-by: Borislav Petkov <bpetkov@suse.de>
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Signed-off-by: Michal Hocko <mhocko@suse.com>
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Signed-off-by: Pawan Gupta <pawan.kumar.gupta@linux.intel.com>
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Signed-off-by: Borislav Petkov <bp@suse.de>
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Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
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Reviewed-by: Josh Poimboeuf <jpoimboe@redhat.com>
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Signed-off-by: Ben Hutchings <ben@decadent.org.uk>
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---
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arch/x86/Kconfig | 45 +++++++++++++++++++++++++++++++++++++++
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arch/x86/kernel/cpu/tsx.c | 22 +++++++++++++------
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2 files changed, 61 insertions(+), 6 deletions(-)
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--- a/arch/x86/Kconfig
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+++ b/arch/x86/Kconfig
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@@ -1903,6 +1903,51 @@ config X86_INTEL_MEMORY_PROTECTION_KEYS
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If unsure, say y.
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+choice
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+ prompt "TSX enable mode"
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+ depends on CPU_SUP_INTEL
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+ default X86_INTEL_TSX_MODE_OFF
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+ help
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+ Intel's TSX (Transactional Synchronization Extensions) feature
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+ allows to optimize locking protocols through lock elision which
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+ can lead to a noticeable performance boost.
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+
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+ On the other hand it has been shown that TSX can be exploited
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+ to form side channel attacks (e.g. TAA) and chances are there
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+ will be more of those attacks discovered in the future.
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+
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+ Therefore TSX is not enabled by default (aka tsx=off). An admin
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+ might override this decision by tsx=on the command line parameter.
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+ Even with TSX enabled, the kernel will attempt to enable the best
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+ possible TAA mitigation setting depending on the microcode available
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+ for the particular machine.
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+
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+ This option allows to set the default tsx mode between tsx=on, =off
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+ and =auto. See Documentation/admin-guide/kernel-parameters.txt for more
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+ details.
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+
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+ Say off if not sure, auto if TSX is in use but it should be used on safe
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+ platforms or on if TSX is in use and the security aspect of tsx is not
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+ relevant.
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+
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+config X86_INTEL_TSX_MODE_OFF
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+ bool "off"
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+ help
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+ TSX is disabled if possible - equals to tsx=off command line parameter.
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+
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+config X86_INTEL_TSX_MODE_ON
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+ bool "on"
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+ help
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+ TSX is always enabled on TSX capable HW - equals the tsx=on command
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+ line parameter.
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+
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+config X86_INTEL_TSX_MODE_AUTO
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+ bool "auto"
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+ help
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+ TSX is enabled on TSX capable HW that is believed to be safe against
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+ side channel attacks- equals the tsx=auto command line parameter.
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+endchoice
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+
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config EFI
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bool "EFI runtime service support"
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depends on ACPI
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--- a/arch/x86/kernel/cpu/tsx.c
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+++ b/arch/x86/kernel/cpu/tsx.c
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@@ -73,6 +73,14 @@ static bool __init tsx_ctrl_is_supported
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return !!(ia32_cap & ARCH_CAP_TSX_CTRL_MSR);
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}
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+static enum tsx_ctrl_states x86_get_tsx_auto_mode(void)
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+{
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+ if (boot_cpu_has_bug(X86_BUG_TAA))
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+ return TSX_CTRL_DISABLE;
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+
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+ return TSX_CTRL_ENABLE;
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+}
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+
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void __init tsx_init(void)
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{
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char arg[5] = {};
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@@ -88,17 +96,19 @@ void __init tsx_init(void)
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} else if (!strcmp(arg, "off")) {
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tsx_ctrl_state = TSX_CTRL_DISABLE;
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} else if (!strcmp(arg, "auto")) {
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- if (boot_cpu_has_bug(X86_BUG_TAA))
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- tsx_ctrl_state = TSX_CTRL_DISABLE;
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- else
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- tsx_ctrl_state = TSX_CTRL_ENABLE;
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+ tsx_ctrl_state = x86_get_tsx_auto_mode();
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} else {
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tsx_ctrl_state = TSX_CTRL_DISABLE;
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pr_err("tsx: invalid option, defaulting to off\n");
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}
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} else {
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- /* tsx= not provided, defaulting to off */
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- tsx_ctrl_state = TSX_CTRL_DISABLE;
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+ /* tsx= not provided */
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+ if (IS_ENABLED(CONFIG_X86_INTEL_TSX_MODE_AUTO))
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+ tsx_ctrl_state = x86_get_tsx_auto_mode();
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+ else if (IS_ENABLED(CONFIG_X86_INTEL_TSX_MODE_OFF))
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+ tsx_ctrl_state = TSX_CTRL_DISABLE;
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+ else
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+ tsx_ctrl_state = TSX_CTRL_ENABLE;
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}
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if (tsx_ctrl_state == TSX_CTRL_DISABLE) {
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