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Merge branch 'x86-pti-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip

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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
This commit is contained in:
Linus Torvalds 2019-11-26 10:11:01 -08:00
commit 53a07a148f
4 changed files with 48 additions and 5 deletions
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7
Documentation/admin-guide/hw-vuln/mds.rst
View File

@ -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
--------------------------

5
Documentation/admin-guide/hw-vuln/tsx_async_abort.rst
View File

@ -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

11
Documentation/admin-guide/kernel-parameters.txt
View File

@ -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

30
arch/x86/kernel/cpu/bugs.c
View File

@ -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]);
}