linux/arch/x86/kernel/probe_roms.c
Linus Torvalds 0c389d89ab maccess: make get_kernel_nofault() check for minimal type compatibility
Now that we've renamed probe_kernel_address() to get_kernel_nofault()
and made it look and behave more in line with get_user(), some of the
subtle type behavior differences end up being more obvious and possibly
dangerous.

When you do

        get_user(val, user_ptr);

the type of the access comes from the "user_ptr" part, and the above
basically acts as

        val = *user_ptr;

by design (except, of course, for the fact that the actual dereference
is done with a user access).

Note how in the above case, the type of the end result comes from the
pointer argument, and then the value is cast to the type of 'val' as
part of the assignment.

So the type of the pointer is ultimately the more important type both
for the access itself.

But 'get_kernel_nofault()' may now _look_ similar, but it behaves very
differently.  When you do

        get_kernel_nofault(val, kernel_ptr);

it behaves like

        val = *(typeof(val) *)kernel_ptr;

except, of course, for the fact that the actual dereference is done with
exception handling so that a faulting access is suppressed and returned
as the error code.

But note how different the casting behavior of the two superficially
similar accesses are: one does the actual access in the size of the type
the pointer points to, while the other does the access in the size of
the target, and ignores the pointer type entirely.

Actually changing get_kernel_nofault() to act like get_user() is almost
certainly the right thing to do eventually, but in the meantime this
patch adds logit to at least verify that the pointer type is compatible
with the type of the result.

In many cases, this involves just casting the pointer to 'void *' to
make it obvious that the type of the pointer is not the important part.
It's not how 'get_user()' acts, but at least the behavioral difference
is now obvious and explicit.

Cc: Christoph Hellwig <hch@lst.de>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2020-06-18 12:10:37 -07:00

270 lines
6.3 KiB
C

// SPDX-License-Identifier: GPL-2.0
#include <linux/sched.h>
#include <linux/mm.h>
#include <linux/uaccess.h>
#include <linux/mmzone.h>
#include <linux/ioport.h>
#include <linux/seq_file.h>
#include <linux/console.h>
#include <linux/init.h>
#include <linux/edd.h>
#include <linux/dmi.h>
#include <linux/pfn.h>
#include <linux/pci.h>
#include <linux/export.h>
#include <asm/probe_roms.h>
#include <asm/pci-direct.h>
#include <asm/e820/api.h>
#include <asm/mmzone.h>
#include <asm/setup.h>
#include <asm/sections.h>
#include <asm/io.h>
#include <asm/setup_arch.h>
static struct resource system_rom_resource = {
.name = "System ROM",
.start = 0xf0000,
.end = 0xfffff,
.flags = IORESOURCE_BUSY | IORESOURCE_READONLY | IORESOURCE_MEM
};
static struct resource extension_rom_resource = {
.name = "Extension ROM",
.start = 0xe0000,
.end = 0xeffff,
.flags = IORESOURCE_BUSY | IORESOURCE_READONLY | IORESOURCE_MEM
};
static struct resource adapter_rom_resources[] = { {
.name = "Adapter ROM",
.start = 0xc8000,
.end = 0,
.flags = IORESOURCE_BUSY | IORESOURCE_READONLY | IORESOURCE_MEM
}, {
.name = "Adapter ROM",
.start = 0,
.end = 0,
.flags = IORESOURCE_BUSY | IORESOURCE_READONLY | IORESOURCE_MEM
}, {
.name = "Adapter ROM",
.start = 0,
.end = 0,
.flags = IORESOURCE_BUSY | IORESOURCE_READONLY | IORESOURCE_MEM
}, {
.name = "Adapter ROM",
.start = 0,
.end = 0,
.flags = IORESOURCE_BUSY | IORESOURCE_READONLY | IORESOURCE_MEM
}, {
.name = "Adapter ROM",
.start = 0,
.end = 0,
.flags = IORESOURCE_BUSY | IORESOURCE_READONLY | IORESOURCE_MEM
}, {
.name = "Adapter ROM",
.start = 0,
.end = 0,
.flags = IORESOURCE_BUSY | IORESOURCE_READONLY | IORESOURCE_MEM
} };
static struct resource video_rom_resource = {
.name = "Video ROM",
.start = 0xc0000,
.end = 0xc7fff,
.flags = IORESOURCE_BUSY | IORESOURCE_READONLY | IORESOURCE_MEM
};
/* does this oprom support the given pci device, or any of the devices
* that the driver supports?
*/
static bool match_id(struct pci_dev *pdev, unsigned short vendor, unsigned short device)
{
struct pci_driver *drv = pdev->driver;
const struct pci_device_id *id;
if (pdev->vendor == vendor && pdev->device == device)
return true;
for (id = drv ? drv->id_table : NULL; id && id->vendor; id++)
if (id->vendor == vendor && id->device == device)
break;
return id && id->vendor;
}
static bool probe_list(struct pci_dev *pdev, unsigned short vendor,
const void *rom_list)
{
unsigned short device;
do {
if (get_kernel_nofault(device, rom_list) != 0)
device = 0;
if (device && match_id(pdev, vendor, device))
break;
rom_list += 2;
} while (device);
return !!device;
}
static struct resource *find_oprom(struct pci_dev *pdev)
{
struct resource *oprom = NULL;
int i;
for (i = 0; i < ARRAY_SIZE(adapter_rom_resources); i++) {
struct resource *res = &adapter_rom_resources[i];
unsigned short offset, vendor, device, list, rev;
const void *rom;
if (res->end == 0)
break;
rom = isa_bus_to_virt(res->start);
if (get_kernel_nofault(offset, rom + 0x18) != 0)
continue;
if (get_kernel_nofault(vendor, rom + offset + 0x4) != 0)
continue;
if (get_kernel_nofault(device, rom + offset + 0x6) != 0)
continue;
if (match_id(pdev, vendor, device)) {
oprom = res;
break;
}
if (get_kernel_nofault(list, rom + offset + 0x8) == 0 &&
get_kernel_nofault(rev, rom + offset + 0xc) == 0 &&
rev >= 3 && list &&
probe_list(pdev, vendor, rom + offset + list)) {
oprom = res;
break;
}
}
return oprom;
}
void __iomem *pci_map_biosrom(struct pci_dev *pdev)
{
struct resource *oprom = find_oprom(pdev);
if (!oprom)
return NULL;
return ioremap(oprom->start, resource_size(oprom));
}
EXPORT_SYMBOL(pci_map_biosrom);
void pci_unmap_biosrom(void __iomem *image)
{
iounmap(image);
}
EXPORT_SYMBOL(pci_unmap_biosrom);
size_t pci_biosrom_size(struct pci_dev *pdev)
{
struct resource *oprom = find_oprom(pdev);
return oprom ? resource_size(oprom) : 0;
}
EXPORT_SYMBOL(pci_biosrom_size);
#define ROMSIGNATURE 0xaa55
static int __init romsignature(const unsigned char *rom)
{
const unsigned short * const ptr = (const unsigned short *)rom;
unsigned short sig;
return get_kernel_nofault(sig, ptr) == 0 && sig == ROMSIGNATURE;
}
static int __init romchecksum(const unsigned char *rom, unsigned long length)
{
unsigned char sum, c;
for (sum = 0; length && get_kernel_nofault(c, rom++) == 0; length--)
sum += c;
return !length && !sum;
}
void __init probe_roms(void)
{
const unsigned char *rom;
unsigned long start, length, upper;
unsigned char c;
int i;
/* video rom */
upper = adapter_rom_resources[0].start;
for (start = video_rom_resource.start; start < upper; start += 2048) {
rom = isa_bus_to_virt(start);
if (!romsignature(rom))
continue;
video_rom_resource.start = start;
if (get_kernel_nofault(c, rom + 2) != 0)
continue;
/* 0 < length <= 0x7f * 512, historically */
length = c * 512;
/* if checksum okay, trust length byte */
if (length && romchecksum(rom, length))
video_rom_resource.end = start + length - 1;
request_resource(&iomem_resource, &video_rom_resource);
break;
}
start = (video_rom_resource.end + 1 + 2047) & ~2047UL;
if (start < upper)
start = upper;
/* system rom */
request_resource(&iomem_resource, &system_rom_resource);
upper = system_rom_resource.start;
/* check for extension rom (ignore length byte!) */
rom = isa_bus_to_virt(extension_rom_resource.start);
if (romsignature(rom)) {
length = resource_size(&extension_rom_resource);
if (romchecksum(rom, length)) {
request_resource(&iomem_resource, &extension_rom_resource);
upper = extension_rom_resource.start;
}
}
/* check for adapter roms on 2k boundaries */
for (i = 0; i < ARRAY_SIZE(adapter_rom_resources) && start < upper; start += 2048) {
rom = isa_bus_to_virt(start);
if (!romsignature(rom))
continue;
if (get_kernel_nofault(c, rom + 2) != 0)
continue;
/* 0 < length <= 0x7f * 512, historically */
length = c * 512;
/* but accept any length that fits if checksum okay */
if (!length || start + length > upper || !romchecksum(rom, length))
continue;
adapter_rom_resources[i].start = start;
adapter_rom_resources[i].end = start + length - 1;
request_resource(&iomem_resource, &adapter_rom_resources[i]);
start = adapter_rom_resources[i++].end & ~2047UL;
}
}