Messages in this thread | | | Subject | Re: [PATCH] x86/speculation: Fix incorrect MDS/TAA mitigation status | From | Waiman Long <> | Date | Thu, 14 Nov 2019 12:53:32 -0500 |
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On 11/14/19 12:45 PM, Borislav Petkov wrote: > On Wed, Nov 13, 2019 at 02:33:50PM -0500, Waiman Long wrote: >> 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 mitigated. 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. >> >> 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. >> >> Signed-off-by: Waiman Long <longman@redhat.com> >> --- >> arch/x86/kernel/cpu/bugs.c | 17 +++++++++++++++-- >> 1 file changed, 15 insertions(+), 2 deletions(-) >> >> diff --git a/arch/x86/kernel/cpu/bugs.c b/arch/x86/kernel/cpu/bugs.c >> index 4c7b0fa15a19..418d41c1fd0d 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. >> + */ > So this changes the dependency of switches so if anything, it should be > properly documented first in all three: > > Documentation/admin-guide/hw-vuln/tsx_async_abort.rst > Documentation/x86/tsx_async_abort.rst > Documentation/admin-guide/kernel-parameters.txt > > However, before we do that, we need to agree on functionality: I agree that the documentation needs to be updated. I am going to do that once we have a consensus of what is the right thing to do. > Will the mitigations be disabled only with *both* =off supplied on the > command line or should the mitigations be disabled when *any* of the two > =off is supplied?
The mitigation is disabled only with BOTH =off supplied or "mitigations=off". This is the current behavior. This patch is just to make sure that vulnerabilities files reflect the actual behavior. Of course, we can change it to disable mitigation with either =off if this is what the consensus turn out to be.
Cheers, Longman
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