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x86/cpu: Add a "tsx=" cmdline option with TSX disabled by default

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Add a kernel cmdline parameter "tsx" to control the Transactional
Synchronization Extensions (TSX) feature. On CPUs that support TSX
control, use "tsx=on|off" to enable or disable TSX. Not specifying this
option is equivalent to "tsx=off". This is because on certain processors
TSX may be used as a part of a speculative side channel attack.

Carve out the TSX controlling functionality into a separate compilation
unit because TSX is a CPU feature while the TSX async abort control
machinery will go to cpu/bugs.c.

 [ bp: - Massage, shorten and clear the arg buffer.
       - Clarifications of the tsx= possible options - Josh.
       - Expand on TSX_CTRL availability - Pawan. ]

Signed-off-by: Pawan Gupta <[email protected]>
Signed-off-by: Borislav Petkov <[email protected]>
Signed-off-by: Thomas Gleixner <[email protected]>
Reviewed-by: Josh Poimboeuf <[email protected]>
This commit is contained in:
Pawan Gupta 2019-10-23 11:01:53 +02:00 • committed by Thomas Gleixner
commit 95c5824f75
6 changed files with 175 additions and 1 deletions
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26
Documentation/admin-guide/kernel-parameters.txt
View file

@ -4848,6 +4848,32 @@
interruptions from clocksource watchdog are not
acceptable).
tsx= [X86] Control Transactional Synchronization
Extensions (TSX) feature in Intel processors that
support TSX control.
This parameter controls the TSX feature. The options are:
on - Enable TSX on the system. Although there are
mitigations for all known security vulnerabilities,
TSX has been known to be an accelerator for
several previous speculation-related CVEs, and
so there may be unknown security risks associated
with leaving it enabled.
off - Disable TSX on the system. (Note that this
option takes effect only on newer CPUs which are
not vulnerable to MDS, i.e., have
MSR_IA32_ARCH_CAPABILITIES.MDS_NO=1 and which get
the new IA32_TSX_CTRL MSR through a microcode
update. This new MSR allows for the reliable
deactivation of the TSX functionality.)
Not specifying this option is equivalent to tsx=off.
See Documentation/admin-guide/hw-vuln/tsx_async_abort.rst
for more details.
turbografx.map[2|3]= [HW,JOY]
TurboGraFX parallel port interface
Format: