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Documentation/srso: Document IBPB aspect and fix formatting

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Add a note about the dependency of the User->User mitigation on the
previous Spectre v2 IBPB selection.

Make the layout moar pretty.

Signed-off-by: Borislav Petkov (AMD) <bp@alien8.de>
Reviewed-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Link: https://lore.kernel.org/r/20230809102700.29449-4-bp@alien8.de
This commit is contained in:
Borislav Petkov (AMD) 2023-08-02 20:07:32 +02:00
parent 0fddfe3382
commit 09f9f37c32
1 changed files with 44 additions and 27 deletions
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71
Documentation/admin-guide/hw-vuln/srso.rst
View file

@ -42,42 +42,59 @@ The sysfs file showing SRSO mitigation status is:
The possible values in this file are:
- 'Not affected' The processor is not vulnerable
* 'Not affected':
- 'Vulnerable: no microcode' The processor is vulnerable, no
microcode extending IBPB functionality
to address the vulnerability has been
applied.
The processor is not vulnerable
- 'Mitigation: microcode' Extended IBPB functionality microcode
patch has been applied. It does not
address User->Kernel and Guest->Host
transitions protection but it does
address User->User and VM->VM attack
vectors.
* 'Vulnerable: no microcode':
(spec_rstack_overflow=microcode)
The processor is vulnerable, no microcode extending IBPB
functionality to address the vulnerability has been applied.
- 'Mitigation: safe RET' Software-only mitigation. It complements
the extended IBPB microcode patch
functionality by addressing User->Kernel
and Guest->Host transitions protection.
* 'Mitigation: microcode':
Selected by default or by
spec_rstack_overflow=safe-ret
Extended IBPB functionality microcode patch has been applied. It does
not address User->Kernel and Guest->Host transitions protection but it
does address User->User and VM->VM attack vectors.
- 'Mitigation: IBPB' Similar protection as "safe RET" above
but employs an IBPB barrier on privilege
domain crossings (User->Kernel,
Guest->Host).
Note that User->User mitigation is controlled by how the IBPB aspect in
the Spectre v2 mitigation is selected:
(spec_rstack_overflow=ibpb)
* conditional IBPB:
where each process can select whether it needs an IBPB issued
around it PR_SPEC_DISABLE/_ENABLE etc, see :doc:`spectre`
* strict:
i.e., always on - by supplying spectre_v2_user=on on the kernel
command line
(spec_rstack_overflow=microcode)
* 'Mitigation: safe RET':
Software-only mitigation. It complements the extended IBPB microcode
patch functionality by addressing User->Kernel and Guest->Host
transitions protection.
Selected by default or by spec_rstack_overflow=safe-ret
* 'Mitigation: IBPB':
Similar protection as "safe RET" above but employs an IBPB barrier on
privilege domain crossings (User->Kernel, Guest->Host).
(spec_rstack_overflow=ibpb)
* 'Mitigation: IBPB on VMEXIT':
Mitigation addressing the cloud provider scenario - the Guest->Host
transitions only.
(spec_rstack_overflow=ibpb-vmexit)
- 'Mitigation: IBPB on VMEXIT' Mitigation addressing the cloud provider
scenario - the Guest->Host transitions
only.
(spec_rstack_overflow=ibpb-vmexit)
In order to exploit vulnerability, an attacker needs to: