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Message-ID: <20220406111751.GA132418@bhelgaas>
Date: Wed, 6 Apr 2022 06:17:51 -0500
From: Bjorn Helgaas <helgaas@...nel.org>
To: David Stevens <stevensd@...omium.org>
Cc: linux-pci@...r.kernel.org, Bjorn Helgaas <bhelgaas@...gle.com>,
Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
linux-kernel@...r.kernel.org, Kees Cook <keescook@...omium.org>
Subject: Re: [RFC] PCI: sysfs: add bypass for config read admin check
[+cc Kees]
On Wed, Apr 06, 2022 at 04:11:31PM +0900, David Stevens wrote:
> 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.
Can you expand this a bit to explain the purpose of this? I guess it
makes "lspci -v" work without having to be root? How much of a
problem is that? Is there some specific use case that needs this
change? Maybe there's some way to address that without having to add
a new parameter that bypasses CAP_SYS_ADMIN.
> 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
>
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