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From:   Stephen Kitt <steve@sk2.org>
To:     linux-kernel@vger.kernel.org
Cc:     Stephen Kitt <steve@sk2.org>, Bjorn Helgaas <bhelgaas@google.com>,
        linux-pci@vger.kernel.org
Subject: [PATCH] PCI/ASPM: Call pcie_aspm_sanity_check() as late as possible
Date:   Thu,  6 Oct 2022 13:59:50 +0200
Message-Id: <20221006115950.821736-1-steve@sk2.org>
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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@sk2.org>
---
 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)
 		return;
@@ -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
-- 
2.30.2