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

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

[Greg Kroah-Hartman]

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.


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

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

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

[Greg Kroah-Hartman]

On Mon, Apr 22, 2024 at 01:00:18PM +0200, Nikolay Borisov wrote:
> 
> 
> 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.

You are right, our fault.  I'll go reject this CVE now, thanks for the
review!

greg k-h