linux-kernel - [RFC] PCI: sysfs: add bypass for config read admin check

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Message-Id: <20220406071131.2930035-1-stevensd@google.com>
Date:   Wed,  6 Apr 2022 16:11:31 +0900
From:   David Stevens <stevensd@...omium.org>
To:     linux-pci@...r.kernel.org
Cc:     Bjorn Helgaas <bhelgaas@...gle.com>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        linux-kernel@...r.kernel.org, David Stevens <stevensd@...omium.org>
Subject: [RFC] PCI: sysfs: add bypass for config read admin check

From: David Stevens <stevensd@...omium.org>

Add a moduleparam that can be set to bypass the check that limits users
without CAP_SYS_ADMIN to only being able to read the first 64 bytes of
the config space. This allows systems without problematic hardware to be
configured to allow users without CAP_SYS_ADMIN to read PCI
capabilities.

Signed-off-by: David Stevens <stevensd@...omium.org>
---
 drivers/pci/pci-sysfs.c | 10 +++++++++-
 1 file changed, 9 insertions(+), 1 deletion(-)

diff --git a/drivers/pci/pci-sysfs.c b/drivers/pci/pci-sysfs.c
index 602f0fb0b007..162423b3c052 100644
--- a/drivers/pci/pci-sysfs.c
+++ b/drivers/pci/pci-sysfs.c
@@ -28,10 +28,17 @@
 #include <linux/pm_runtime.h>
 #include <linux/msi.h>
 #include <linux/of.h>
+#include <linux/moduleparam.h>
 #include "pci.h"
 
 static int sysfs_initialized;	/* = 0 */
 
+static bool allow_unsafe_config_reads;
+module_param_named(allow_unsafe_config_reads,
+		   allow_unsafe_config_reads, bool, 0644);
+MODULE_PARM_DESC(allow_unsafe_config_reads,
+		 "Enable full read access to config space without CAP_SYS_ADMIN.");
+
 /* show configuration fields */
 #define pci_config_attr(field, format_string)				\
 static ssize_t								\
@@ -696,7 +703,8 @@ static ssize_t pci_read_config(struct file *filp, struct kobject *kobj,
 	u8 *data = (u8 *) buf;
 
 	/* Several chips lock up trying to read undefined config space */
-	if (file_ns_capable(filp, &init_user_ns, CAP_SYS_ADMIN))
+	if (allow_unsafe_config_reads ||
+	    file_ns_capable(filp, &init_user_ns, CAP_SYS_ADMIN))
 		size = dev->cfg_size;
 	else if (dev->hdr_type == PCI_HEADER_TYPE_CARDBUS)
 		size = 128;
-- 
2.35.1.1094.g7c7d902a7c-goog