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authorLinus Torvalds <torvalds@linux-foundation.org>2019-11-26 10:11:01 -0800
committerLinus Torvalds <torvalds@linux-foundation.org>2019-11-26 10:11:01 -0800
commit53a07a148fd05dc6d317745688270bc79fe73121 (patch)
treebbe1eca87d45a6d96e38e6821f84d478466d403a
parentda42761df5ceed2f8b0527bc4c1b2760be45ddb9 (diff)
parentcd5a2aa89e847bdda7b62029d94e95488d73f6b2 (diff)
downloadlinux-53a07a148fd05dc6d317745688270bc79fe73121.tar.bz2
Merge branch 'x86-pti-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip
Pull x86 PTI updates from Ingo Molnar: "Fix reporting bugs of the MDS and TAA mitigation status, if one or both are set via a boot option. No change to mitigation behavior intended" * 'x86-pti-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip: x86/speculation: Fix redundant MDS mitigation message x86/speculation: Fix incorrect MDS/TAA mitigation status
-rw-r--r--Documentation/admin-guide/hw-vuln/mds.rst7
-rw-r--r--Documentation/admin-guide/hw-vuln/tsx_async_abort.rst5
-rw-r--r--Documentation/admin-guide/kernel-parameters.txt11
-rw-r--r--arch/x86/kernel/cpu/bugs.c30
4 files changed, 48 insertions, 5 deletions
diff --git a/Documentation/admin-guide/hw-vuln/mds.rst b/Documentation/admin-guide/hw-vuln/mds.rst
index e3a796c0d3a2..2d19c9f4c1fe 100644
--- a/Documentation/admin-guide/hw-vuln/mds.rst
+++ b/Documentation/admin-guide/hw-vuln/mds.rst
@@ -265,8 +265,11 @@ time with the option "mds=". The valid arguments for this option are:
============ =============================================================
-Not specifying this option is equivalent to "mds=full".
-
+Not specifying this option is equivalent to "mds=full". For processors
+that are affected by both TAA (TSX Asynchronous Abort) and MDS,
+specifying just "mds=off" without an accompanying "tsx_async_abort=off"
+will have no effect as the same mitigation is used for both
+vulnerabilities.
Mitigation selection guide
--------------------------
diff --git a/Documentation/admin-guide/hw-vuln/tsx_async_abort.rst b/Documentation/admin-guide/hw-vuln/tsx_async_abort.rst
index fddbd7579c53..af6865b822d2 100644
--- a/Documentation/admin-guide/hw-vuln/tsx_async_abort.rst
+++ b/Documentation/admin-guide/hw-vuln/tsx_async_abort.rst
@@ -174,7 +174,10 @@ the option "tsx_async_abort=". The valid arguments for this option are:
CPU is not vulnerable to cross-thread TAA attacks.
============ =============================================================
-Not specifying this option is equivalent to "tsx_async_abort=full".
+Not specifying this option is equivalent to "tsx_async_abort=full". For
+processors that are affected by both TAA and MDS, specifying just
+"tsx_async_abort=off" without an accompanying "mds=off" will have no
+effect as the same mitigation is used for both vulnerabilities.
The kernel command line also allows to control the TSX feature using the
parameter "tsx=" on CPUs which support TSX control. MSR_IA32_TSX_CTRL is used
diff --git a/Documentation/admin-guide/kernel-parameters.txt b/Documentation/admin-guide/kernel-parameters.txt
index 9b847f06cb19..a0a4732eedbb 100644
--- a/Documentation/admin-guide/kernel-parameters.txt
+++ b/Documentation/admin-guide/kernel-parameters.txt
@@ -2473,6 +2473,12 @@
SMT on vulnerable CPUs
off - Unconditionally disable MDS mitigation
+ On TAA-affected machines, mds=off can be prevented by
+ an active TAA mitigation as both vulnerabilities are
+ mitigated with the same mechanism so in order to disable
+ this mitigation, you need to specify tsx_async_abort=off
+ too.
+
Not specifying this option is equivalent to
mds=full.
@@ -4931,6 +4937,11 @@
vulnerable to cross-thread TAA attacks.
off - Unconditionally disable TAA mitigation
+ On MDS-affected machines, tsx_async_abort=off can be
+ prevented by an active MDS mitigation as both vulnerabilities
+ are mitigated with the same mechanism so in order to disable
+ this mitigation, you need to specify mds=off too.
+
Not specifying this option is equivalent to
tsx_async_abort=full. On CPUs which are MDS affected
and deploy MDS mitigation, TAA mitigation is not
diff --git a/arch/x86/kernel/cpu/bugs.c b/arch/x86/kernel/cpu/bugs.c
index 4c7b0fa15a19..8bf64899f56a 100644
--- a/arch/x86/kernel/cpu/bugs.c
+++ b/arch/x86/kernel/cpu/bugs.c
@@ -39,6 +39,7 @@ static void __init spectre_v2_select_mitigation(void);
static void __init ssb_select_mitigation(void);
static void __init l1tf_select_mitigation(void);
static void __init mds_select_mitigation(void);
+static void __init mds_print_mitigation(void);
static void __init taa_select_mitigation(void);
/* The base value of the SPEC_CTRL MSR that always has to be preserved. */
@@ -108,6 +109,12 @@ void __init check_bugs(void)
mds_select_mitigation();
taa_select_mitigation();
+ /*
+ * As MDS and TAA mitigations are inter-related, print MDS
+ * mitigation until after TAA mitigation selection is done.
+ */
+ mds_print_mitigation();
+
arch_smt_update();
#ifdef CONFIG_X86_32
@@ -245,6 +252,12 @@ static void __init mds_select_mitigation(void)
(mds_nosmt || cpu_mitigations_auto_nosmt()))
cpu_smt_disable(false);
}
+}
+
+static void __init mds_print_mitigation(void)
+{
+ if (!boot_cpu_has_bug(X86_BUG_MDS) || cpu_mitigations_off())
+ return;
pr_info("%s\n", mds_strings[mds_mitigation]);
}
@@ -304,8 +317,12 @@ static void __init taa_select_mitigation(void)
return;
}
- /* TAA mitigation is turned off on the cmdline (tsx_async_abort=off) */
- if (taa_mitigation == TAA_MITIGATION_OFF)
+ /*
+ * TAA mitigation via VERW is turned off if both
+ * tsx_async_abort=off and mds=off are specified.
+ */
+ if (taa_mitigation == TAA_MITIGATION_OFF &&
+ mds_mitigation == MDS_MITIGATION_OFF)
goto out;
if (boot_cpu_has(X86_FEATURE_MD_CLEAR))
@@ -339,6 +356,15 @@ static void __init taa_select_mitigation(void)
if (taa_nosmt || cpu_mitigations_auto_nosmt())
cpu_smt_disable(false);
+ /*
+ * Update MDS mitigation, if necessary, as the mds_user_clear is
+ * now enabled for TAA mitigation.
+ */
+ if (mds_mitigation == MDS_MITIGATION_OFF &&
+ boot_cpu_has_bug(X86_BUG_MDS)) {
+ mds_mitigation = MDS_MITIGATION_FULL;
+ mds_select_mitigation();
+ }
out:
pr_info("%s\n", taa_strings[taa_mitigation]);
}