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Documentation/hw-vuln: Update spectre doc

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Update the doc with the new fun.

  [ bp: Massage commit message. ]

Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Signed-off-by: Borislav Petkov <bp@suse.de>
Reviewed-by: Thomas Gleixner <tglx@linutronix.de>
This commit is contained in:
Peter Zijlstra 2022-02-16 20:57:02 +01:00 committed by Borislav Petkov
parent 1e19da8522
commit 5ad3eb1132
2 changed files with 36 additions and 16 deletions
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44
Documentation/admin-guide/hw-vuln/spectre.rst
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@ -131,6 +131,19 @@ steer its indirect branch speculations to gadget code, and measure the
speculative execution's side effects left in level 1 cache to infer the
victim's data.
Yet another variant 2 attack vector is for the attacker to poison the
Branch History Buffer (BHB) to speculatively steer an indirect branch
to a specific Branch Target Buffer (BTB) entry, even if the entry isn't
associated with the source address of the indirect branch. Specifically,
the BHB might be shared across privilege levels even in the presence of
Enhanced IBRS.
Currently the only known real-world BHB attack vector is via
unprivileged eBPF. Therefore, it's highly recommended to not enable
unprivileged eBPF, especially when eIBRS is used (without retpolines).
For a full mitigation against BHB attacks, it's recommended to use
retpolines (or eIBRS combined with retpolines).
Attack scenarios
----------------
@ -364,13 +377,15 @@ The possible values in this file are:
- Kernel status:
==================================== =================================
'Not affected' The processor is not vulnerable
'Vulnerable' Vulnerable, no mitigation
'Mitigation: Full generic retpoline' Software-focused mitigation
'Mitigation: Full AMD retpoline' AMD-specific software mitigation
'Mitigation: Enhanced IBRS' Hardware-focused mitigation
==================================== =================================
======================================== =================================
'Not affected' The processor is not vulnerable
'Mitigation: None' Vulnerable, no mitigation
'Mitigation: Retpolines' Use Retpoline thunks
'Mitigation: LFENCE' Use LFENCE instructions
'Mitigation: Enhanced IBRS' Hardware-focused mitigation
'Mitigation: Enhanced IBRS + Retpolines' Hardware-focused + Retpolines
'Mitigation: Enhanced IBRS + LFENCE' Hardware-focused + LFENCE
======================================== =================================
- Firmware status: Show if Indirect Branch Restricted Speculation (IBRS) is
used to protect against Spectre variant 2 attacks when calling firmware (x86 only).
@ -583,12 +598,13 @@ kernel command line.
Specific mitigations can also be selected manually:
retpoline
replace indirect branches
retpoline,generic
google's original retpoline
retpoline,amd
AMD-specific minimal thunk
retpoline auto pick between generic,lfence
retpoline,generic Retpolines
retpoline,lfence LFENCE; indirect branch
retpoline,amd alias for retpoline,lfence
eibrs enhanced IBRS
eibrs,retpoline enhanced IBRS + Retpolines
eibrs,lfence enhanced IBRS + LFENCE
Not specifying this option is equivalent to
spectre_v2=auto.
@ -599,7 +615,7 @@ kernel command line.
spectre_v2=off. Spectre variant 1 mitigations
cannot be disabled.
For spectre_v2_user see :doc:`/admin-guide/kernel-parameters`.
For spectre_v2_user see Documentation/admin-guide/kernel-parameters.txt
Mitigation selection guide
--------------------------

8
Documentation/admin-guide/kernel-parameters.txt
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@ -5361,8 +5361,12 @@
Specific mitigations can also be selected manually:
retpoline - replace indirect branches
retpoline,generic - google's original retpoline
retpoline,amd - AMD-specific minimal thunk
retpoline,generic - Retpolines
retpoline,lfence - LFENCE; indirect branch
retpoline,amd - alias for retpoline,lfence
eibrs - enhanced IBRS
eibrs,retpoline - enhanced IBRS + Retpolines
eibrs,lfence - enhanced IBRS + LFENCE
Not specifying this option is equivalent to
spectre_v2=auto.