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Peter Anvin" Cc: Tomita Moeko , linux-pci@vger.kernel.org, linux-kernel@vger.kernel.org Subject: [PATCH v2] x86/pci: Check signature before assigning shadow ROM Date: Thu, 16 Oct 2025 16:19:00 +0800 Message-ID: <20251016081900.7129-1-tomitamoeko@gmail.com> X-Mailer: git-send-email 2.51.0 Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: quoted-printable Content-Type: text/plain; charset="utf-8" Recent IGD platforms without VBIOS or UEFI CSM support do not contain VGA ROM at 0xC0000. Check whether the VGA ROM region is a valid PCI option ROM with 0xAA55 signature before assigning the shadow ROM to the default PCI VGA controller. Signed-off-by: Tomita Moeko --- Changelog: v2: * Use memmap() instead of iomap() as the shadow ROM is copied to RAM by BIOS * Only map the first 2 bytes for the signature check. Link: https://lore.kernel.org/all/20250406090835.7721-1-tomitamoeko@gmail.c= om/ arch/x86/pci/fixup.c | 12 ++++++++++++ 1 file changed, 12 insertions(+) diff --git a/arch/x86/pci/fixup.c b/arch/x86/pci/fixup.c index 25076a5acd96..10dce90e0e00 100644 --- a/arch/x86/pci/fixup.c +++ b/arch/x86/pci/fixup.c @@ -357,6 +357,18 @@ static void pci_fixup_video(struct pci_dev *pdev) struct pci_bus *bus; u16 config; struct resource *res; + void *rom; + u16 sig; + + /* Does VBIOS region contain a valid PCI ROM? */ + rom =3D memremap(0xC0000, sizeof(sig), MEMREMAP_WB); + if (!rom) + return; + + memcpy(&sig, rom, sizeof(sig)); + memunmap(rom); + if (sig !=3D 0xAA55) + return; =20 /* Is VGA routed to us? */ bus =3D pdev->bus; --=20 2.51.0