[PATCH] PCI/ASPM: Call pcie_aspm_sanity_check() as late as possible

From: Stephen Kitt
Date: Thu Oct 06 2022 - 11:40:07 EST

In pcie_aspm_init_link_state(), a number of checks are made to
determine whether the function should proceed, before the result of
the call to pcie_aspm_sanity_check() is actually used. The latter
function doesn't change any state, it only reports a result, so
calling it later doesn't make any difference to the state of the
devices or the information we have about them. But having the call
early reportedly can cause null-pointer dereferences; see
https://unix.stackexchange.com/q/322337 for one example with
pcie_aspm=off (this was reported in 2016, but the relevant code hasn't
changed since then).

This moves the call to pcie_aspm_sanity_check() just before the result
is actually used, giving all the other checks a chance to run first.

Signed-off-by: Stephen Kitt <steve@xxxxxxx>
drivers/pci/pcie/aspm.c | 3 ++-
1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/drivers/pci/pcie/aspm.c b/drivers/pci/pcie/aspm.c
index a8aec190986c..38df439568b7 100644
--- a/drivers/pci/pcie/aspm.c
+++ b/drivers/pci/pcie/aspm.c
@@ -889,7 +889,7 @@ static void pcie_aspm_update_sysfs_visibility(struct pci_dev *pdev)
void pcie_aspm_init_link_state(struct pci_dev *pdev)
struct pcie_link_state *link;
- int blacklist = !!pcie_aspm_sanity_check(pdev);
+ int blacklist;

if (!aspm_support_enabled)
@@ -923,6 +923,7 @@ void pcie_aspm_init_link_state(struct pci_dev *pdev)
* upstream links also because capable state of them can be
* update through pcie_aspm_cap_init().
+ blacklist = !!pcie_aspm_sanity_check(pdev);
pcie_aspm_cap_init(link, blacklist);

/* Setup initial Clock PM state */

base-commit: 833477fce7a14d43ae4c07f8ddc32fa5119471a2