Re: [PATCH RFC v2] HID: amd_sfh: Validate PCI BAR size before mapping

[Slawomir Stepien <sst@poczta.fm>]

On sie 26, 2026 08:17, syzbot wrote:
> The amd_sfh driver maps PCI BAR 2 using pcim_iomap_regions() and
> subsequently accesses MMIO registers at offsets up to 0x10958 (e.g.,
> AMD_P2C_MSG3 at 0x1068C). However, the driver never validates that the BAR
> size is large enough to cover these accesses. If the driver is bound to a
> device with a smaller BAR 2, this leads to an out-of-bounds memory access
> and a page fault during the probe function.
> 
> For example, a page fault can occur when reading from privdata->mmio +
> AMD_P2C_MSG3 in mp2_select_ops():
> 
>   BUG: unable to handle page fault for address: ffffc9000390368c
>   PGD 100000067 P4D 100000067 PUD 1012c1067 PMD 105b64067 PTE 0
>   Oops: Oops: 0000 [#1] SMP KASAN NOPTI
>   RIP: 0010:readl arch/x86/include/asm/io.h:59 [inline]
>   RIP: 0010:mp2_select_ops drivers/hid/amd-sfh-hid/amd_sfh_pcie.c:282
>   [inline]
>   RIP: 0010:amd_mp2_pci_probe+0x337/0x5f0
>   drivers/hid/amd-sfh-hid/amd_sfh_pcie.c:487
>   Call Trace:
>    <TASK>
>    local_pci_probe drivers/pci/pci-driver.c:332 [inline]
>    pci_call_probe drivers/pci/pci-driver.c:394 [inline]
>    __pci_device_probe drivers/pci/pci-driver.c:455 [inline]
>    pci_device_probe+0x431/0xc90 drivers/pci/pci-driver.c:489
> 
> Fix this by verifying that the length of BAR 2 is at least 128KB before
> attempting to map it. Since the maximum accessed offset is 0x10958, and PCI
> BAR sizes are powers of 2, any legitimate hardware will have a BAR size of
> at least 128KB.
> 
> Fixes: 4f567b9f8141 ("SFH: PCIe driver to add support of AMD sensor fusion hub")
> Assisted-by: Gemini:gemini-3.7-flash Gemini:gemini-3.1-pro-preview syzbot
> Reported-by: syzbot+4eadd4dfe9e66522bae8@syzkaller.appspotmail.com
> Closes: https://syzkaller.appspot.com/bug?extid=4eadd4dfe9e66522bae8
> Link: https://syzkaller.appspot.com/ai_job?id=ae80612d-4fc5-4b7a-83bb-894e0a14dc5e
> To: "Basavaraj Natikar" <basavaraj.natikar@amd.com>
> To: "Benjamin Tissoires" <bentiss@kernel.org>
> To: "Jiri Kosina" <jikos@kernel.org>
> To: <linux-input@vger.kernel.org>
> To: "Sandeep Singh" <sandeep.singh@amd.com>
> Cc: <linux-kernel@vger.kernel.org>
> Cc: "Mario Limonciello (AMD)" <superm1@kernel.org>
> 
> ---
> v2:
> - Define AMD_SFH_MIN_BAR_SIZE macro instead of hardcoded 128 * 1024
> - Use AMD_SFH_MIN_BAR_SIZE in amd_sfh1_1_init()
> 
> v1:
> https://lore.kernel.org/all/f83daf97-4762-4a67-bac7-615b34d1b661@mail.kernel.org/T/
> ---
> diff --git a/drivers/hid/amd-sfh-hid/amd_sfh_common.h b/drivers/hid/amd-sfh-hid/amd_sfh_common.h
> index 78f830c13..c0c324565 100644
> --- a/drivers/hid/amd-sfh-hid/amd_sfh_common.h
> +++ b/drivers/hid/amd-sfh-hid/amd_sfh_common.h
> @@ -17,6 +17,8 @@
>  #define PCI_DEVICE_ID_AMD_MP2		0x15E4
>  #define PCI_DEVICE_ID_AMD_MP2_1_1	0x164A
>  
> +#define AMD_SFH_MIN_BAR_SIZE		(128 * 1024)
> +
>  #define AMD_C2P_MSG(regno) (0x10500 + ((regno) * 4))
>  #define AMD_P2C_MSG(regno) (0x10680 + ((regno) * 4))
>  
> diff --git a/drivers/hid/amd-sfh-hid/amd_sfh_pcie.c b/drivers/hid/amd-sfh-hid/amd_sfh_pcie.c
> index 4b81cebdc..d870585a0 100644
> --- a/drivers/hid/amd-sfh-hid/amd_sfh_pcie.c
> +++ b/drivers/hid/amd-sfh-hid/amd_sfh_pcie.c
> @@ -451,6 +451,11 @@ static int amd_mp2_pci_probe(struct pci_dev *pdev, const struct pci_device_id *i
>  	if (rc)
>  		return rc;

Can you also add check for IORESOURCE_MEM using pci_resource_flags() here? Just to be safe.

> +	if (pci_resource_len(pdev, 2) < AMD_SFH_MIN_BAR_SIZE) {
> +		dev_err(&pdev->dev, "BAR 2 is too small\n");
> +		return -EINVAL;
> +	}
> +
>  	rc = pcim_iomap_regions(pdev, BIT(2), DRIVER_NAME);
>  	if (rc)
>  		return rc;
> diff --git a/drivers/hid/amd-sfh-hid/sfh1_1/amd_sfh_init.c b/drivers/hid/amd-sfh-hid/sfh1_1/amd_sfh_init.c
> index b0bab2a1d..0afc596b5 100644
> --- a/drivers/hid/amd-sfh-hid/sfh1_1/amd_sfh_init.c
> +++ b/drivers/hid/amd-sfh-hid/sfh1_1/amd_sfh_init.c
> @@ -388,12 +388,12 @@ int amd_sfh1_1_init(struct amd_mp2_dev *mp2)
>  	int rc;
>  
>  	phy_base <<= 21;
> -	if (!devm_request_mem_region(dev, phy_base, 128 * 1024, "amd_sfh")) {
> +	if (!devm_request_mem_region(dev, phy_base, AMD_SFH_MIN_BAR_SIZE, "amd_sfh")) {

Hm this isn't the BAR2, so using here AMD_SFH_MIN_BAR_SIZE is misleading. Do you agree? Maybe leave
it as it is?

>  		dev_dbg(dev, "can't reserve mmio registers\n");
>  		return -ENOMEM;
>  	}
>  
> -	mp2->vsbase = devm_ioremap(dev, phy_base, 128 * 1024);
> +	mp2->vsbase = devm_ioremap(dev, phy_base, AMD_SFH_MIN_BAR_SIZE);

ditto

>  	if (!mp2->vsbase) {
>  		dev_dbg(dev, "failed to remap vsbase\n");
>  		return -ENOMEM;
> 
> 
> base-commit: db2ddb87143519e20a95aa36c60b36107b736a58

-- 
Slawomir Stepien