Public bug reported:
This bug targets the linux-amd-embedded kernel (Ubuntu 26.04 Resolute,
7.0, amd64). linux-amd-embedded is not yet available in the archive, so
the bug is filed against the linux package for now.
[Impact]
Two issues in the AMD node / SMN code (arch/x86/kernel/amd_node.c):
* On virtualized systems the number of nodes does not have to match the
number of AMD PCI roots. On a Xen PVH dom0, roots_per_node can be
calculated as 0, which leads to a divide by zero in amd_smn_init().
* amd_smn_read()/amd_smn_write() are exported and always available, even
if amd_smn_init() fails. In that case 'amd_roots' is NULL and
__amd_smn_rw() can dereference it.
Both fixes are tagged for stable upstream, but they are not part of the
7.0 stable series.
[Fix]
Cherry-pick the following commits from mainline (v7.3-rc3) into
linux-amd-embedded:
* 72bd92bd8190 ("x86/amd_node: Avoid divide by zero on virtualized systems")
* aefdbd574a36 ("x86/amd_node: Fix potential NULL pointer dereference")
[Test Plan]
* Build the linux-amd-embedded kernel for all flavours.
* Boot the kernel in an LXD VM.
[Where problems could occur]
The changes are limited to the SMN initialization and access paths in
arch/x86/kernel/amd_node.c. A regression could affect drivers using SMN
access on AMD systems, e.g. SMN reads or writes returning an error
instead of data.
** Affects: linux (Ubuntu)
Importance: Undecided
Status: New
** Affects: linux (Ubuntu Resolute)
Importance: High
Assignee: Krystian Kaniewski (kkaniewski)
Status: Confirmed
** Also affects: linux (Ubuntu Resolute)
Importance: Undecided
Status: New
** Changed in: linux (Ubuntu Resolute)
Status: New => Confirmed
** Changed in: linux (Ubuntu Resolute)
Assignee: (unassigned) => Krystian Kaniewski (kkaniewski)
** Changed in: linux (Ubuntu Resolute)
Importance: Undecided => High
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https://bugs.launchpad.net/bugs/2173540
Title:
linux-amd-embedded: x86/amd_node: Fix divide by zero on virtualized
systems and potential NULL pointer dereference
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