From 64870ed1b12e235cfca3f6c6da75b542c973ff78 Mon Sep 17 00:00:00 2001 From: Waiman Long Date: Fri, 15 Nov 2019 11:14:44 -0500 Subject: x86/speculation: Fix incorrect MDS/TAA mitigation status 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 Signed-off-by: Borislav Petkov Cc: Greg Kroah-Hartman Cc: "H. Peter Anvin" Cc: Ingo Molnar Cc: Jiri Kosina Cc: Jonathan Corbet Cc: Josh Poimboeuf Cc: linux-doc@vger.kernel.org Cc: Mark Gross Cc: Cc: Pawan Gupta Cc: Peter Zijlstra Cc: Thomas Gleixner Cc: Tim Chen Cc: Tony Luck Cc: Tyler Hicks Cc: x86-ml Link: https://lkml.kernel.org/r/20191115161445.30809-2-longman@redhat.com --- Documentation/admin-guide/hw-vuln/mds.rst | 7 +++++-- Documentation/admin-guide/hw-vuln/tsx_async_abort.rst | 5 ++++- Documentation/admin-guide/kernel-parameters.txt | 11 +++++++++++ 3 files changed, 20 insertions(+), 3 deletions(-) (limited to 'Documentation/admin-guide') 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 8dee8f68fe15..9983ac73b66d 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 -- cgit v1.2.3