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authorWaiman Long <longman@redhat.com>2019-11-15 11:14:44 -0500
committerGreg Kroah-Hartman <gregkh@linuxfoundation.org>2019-12-01 09:14:22 +0100
commitd68d0c043eaa7d2f3e1ef3070116076983026fd5 (patch)
tree132dc1bf6188f02df1bea27c00f5eb089bd851d3
parentfbb0e381e73094a1288cd5ec459e853ed995c358 (diff)
x86/speculation: Fix incorrect MDS/TAA mitigation status
commit 64870ed1b12e235cfca3f6c6da75b542c973ff78 upstream. For MDS vulnerable processors with TSX support, enabling either MDS or TAA mitigations will enable the use of VERW to flush internal processor buffers at the right code path. IOW, they are either both mitigated or both not. However, if the command line options are inconsistent, the vulnerabilites sysfs files may not report the mitigation status correctly. For example, with only the "mds=off" option: vulnerabilities/mds:Vulnerable; SMT vulnerable vulnerabilities/tsx_async_abort:Mitigation: Clear CPU buffers; SMT vulnerable The mds vulnerabilities file has wrong status in this case. Similarly, the taa vulnerability file will be wrong with mds mitigation on, but taa off. Change taa_select_mitigation() to sync up the two mitigation status and have them turned off if both "mds=off" and "tsx_async_abort=off" are present. Update documentation to emphasize the fact that both "mds=off" and "tsx_async_abort=off" have to be specified together for processors that are affected by both TAA and MDS to be effective. [ bp: Massage and add kernel-parameters.txt change too. ] Fixes: 1b42f017415b ("x86/speculation/taa: Add mitigation for TSX Async Abort") Signed-off-by: Waiman Long <longman@redhat.com> Signed-off-by: Borislav Petkov <bp@suse.de> Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org> Cc: "H. Peter Anvin" <hpa@zytor.com> Cc: Ingo Molnar <mingo@redhat.com> Cc: Jiri Kosina <jkosina@suse.cz> Cc: Jonathan Corbet <corbet@lwn.net> Cc: Josh Poimboeuf <jpoimboe@redhat.com> Cc: linux-doc@vger.kernel.org Cc: Mark Gross <mgross@linux.intel.com> Cc: <stable@vger.kernel.org> Cc: Pawan Gupta <pawan.kumar.gupta@linux.intel.com> Cc: Peter Zijlstra <peterz@infradead.org> Cc: Thomas Gleixner <tglx@linutronix.de> Cc: Tim Chen <tim.c.chen@linux.intel.com> Cc: Tony Luck <tony.luck@intel.com> Cc: Tyler Hicks <tyhicks@canonical.com> Cc: x86-ml <x86@kernel.org> Link: https://lkml.kernel.org/r/20191115161445.30809-2-longman@redhat.com Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
-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.c17
4 files changed, 35 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 05596e05bc71..b0da6050a254 100644
--- a/Documentation/admin-guide/kernel-parameters.txt
+++ b/Documentation/admin-guide/kernel-parameters.txt
@@ -2254,6 +2254,12 @@
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.
@@ -4588,6 +4594,11 @@
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 8596811843cc..c065e7f5f62f 100644
--- a/arch/x86/kernel/cpu/bugs.c
+++ b/arch/x86/kernel/cpu/bugs.c
@@ -304,8 +304,12 @@ 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 +343,15 @@ 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]);
}