19 Aug
2022
19 Aug
'22
11:02 a.m.
On Fri, 2022-08-19 at 10:47 +0200, Peter Zijlstra wrote:
On Fri, Aug 19, 2022 at 02:33:08AM +0200, Ben Hutchings wrote:
From: Ben Hutchings benh@debian.org
The mitigation for PBRSB includes adding LFENCE instructions to the RSB filling sequence. However, RSB filling is done on some older CPUs that don't support the LFENCE instruction.
Wait; what? There are chips that enable the RSB mitigations and DONT have LFENCE ?!?
Yes, X86_FEATURE_RSB_CTXSW is enabled if any other Spectre v2 mitigation is enabled. And all Intel family 6 (except some early Atoms) and AMD family 5+ get Spectre v2 mitigation by default.
Ben.
--
Ben Hutchings
Beware of bugs in the above code;
I have only proved it correct, not tried it. - Donald Knuth