Re: CVE-2023-52575: x86/srso: Fix SBPB enablement for spec_rstack_overflow=off

[Nikolay Borisov]

On 2.03.24 г. 23:00 ч., Greg Kroah-Hartman wrote:
> Description
> ===========
>
> In the Linux kernel, the following vulnerability has been resolved:
>
> x86/srso: Fix SBPB enablement for spec_rstack_overflow=off
>
> If the user has requested no SRSO mitigation, other mitigations can use
> the lighter-weight SBPB instead of IBPB.
>
> The Linux kernel CVE team has assigned CVE-2023-52575 to this issue.

I'd like to dispute this as this isn't a CVE but a mere performance 
optimization in case spec_rstack_overflow is disabled. Without this 
patch in case spec_rstack_overflow is disabled the kernel will simply 
use the heavier ibpb but that won't have effect on correctness.

> Affected and fixed versions
> ===========================
>
> 	Issue introduced in 5.10.189 with commit 8457fb5740b1 and fixed in 5.10.198 with commit ae806c74c063
> 	Issue introduced in 5.15.125 with commit 153f9a7b02d4 and fixed in 5.15.134 with commit 13ea4b92e875
> 	Issue introduced in 6.1.44 with commit 4f25355540ad and fixed in 6.1.56 with commit adbcec23c842
> 	Issue introduced in 6.5 with commit fb3bd914b3ec and fixed in 6.5.6 with commit e3cb8b2c391b
> 	Issue introduced in 6.5 with commit fb3bd914b3ec and fixed in 6.6 with commit 01b057b2f4cc
>
> Please see https://www.kernel.org or a full list of currently supported
> kernel versions by the kernel community.
>
> Unaffected versions might change over time as fixes are backported to
> older supported kernel versions.  The official CVE entry at
> 	https://cve.org/CVERecord/?id=CVE-2023-52575
> will be updated if fixes are backported, please check that for the most
> up to date information about this issue.
>
>
> Affected files
> ==============
>
> The file(s) affected by this issue are:
> 	arch/x86/kernel/cpu/bugs.c
>
>
> Mitigation
> ==========
>
> The Linux kernel CVE team recommends that you update to the latest
> stable kernel version for this, and many other bugfixes.  Individual
> changes are never tested alone, but rather are part of a larger kernel
> release.  Cherry-picking individual commits is not recommended or
> supported by the Linux kernel community at all.  If however, updating to
> the latest release is impossible, the individual changes to resolve this
> issue can be found at these commits:
> 	https://git.kernel.org/stable/c/ae806c74c0634b0c23855066d8ba28d850fd1260
> 	https://git.kernel.org/stable/c/13ea4b92e8759d2f6c330a73cde31ad9c313021b
> 	https://git.kernel.org/stable/c/adbcec23c8423e3d5df1839c5ae91599dcf703cb
> 	https://git.kernel.org/stable/c/e3cb8b2c391b1f287eb76df4ba37880f4ea56d8a
> 	https://git.kernel.org/stable/c/01b057b2f4cc2d905a0bd92195657dbd9a7005ab