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x86/efi-bgrt: Fix kernel panic when mapping BGRT data
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Starting with this commit 35eb8b81edd4 ("x86/efi: Build our own page
table structures") efi regions have a separate page directory called
"efi_pgd". In order to access any efi region we have to first shift %cr3
to this page table. In the bgrt code we are trying to copy bgrt_header
and image, but these regions fall under "EFI_BOOT_SERVICES_DATA"
and to access these regions we have to shift %cr3 to efi_pgd and not
doing so will cause page fault as shown below.

[    0.251599] Last level dTLB entries: 4KB 64, 2MB 0, 4MB 0, 1GB 4
[    0.259126] Freeing SMP alternatives memory: 32K (ffffffff8230e000 - ffffffff82316000)
[    0.271803] BUG: unable to handle kernel paging request at fffffffefce35002
[    0.279740] IP: [<ffffffff821bca49>] efi_bgrt_init+0x144/0x1fd
[    0.286383] PGD 300f067 PUD 0
[    0.289879] Oops: 0000 [#1] SMP
[    0.293566] Modules linked in:
[    0.297039] CPU: 0 PID: 0 Comm: swapper/0 Not tainted 4.4.0-rc1-eywa-eywa-built-in-47041+ #2
[    0.306619] Hardware name: Intel Corporation Skylake Client platform/Skylake Y LPDDR3 RVP3, BIOS SKLSE2R1.R00.B104.B01.1511110114 11/11/2015
[    0.320925] task: ffffffff820134c0 ti: ffffffff82000000 task.ti: ffffffff82000000
[    0.329420] RIP: 0010:[<ffffffff821bca49>]  [<ffffffff821bca49>] efi_bgrt_init+0x144/0x1fd
[    0.338821] RSP: 0000:ffffffff82003f18  EFLAGS: 00010246
[    0.344852] RAX: fffffffefce35000 RBX: fffffffefce35000 RCX: fffffffefce2b000
[    0.352952] RDX: 000000008a82b000 RSI: ffffffff8235bb80 RDI: 000000008a835000
[    0.361050] RBP: ffffffff82003f30 R08: 000000008a865000 R09: ffffffffff202850
[    0.369149] R10: ffffffff811ad62f R11: 0000000000000000 R12: 0000000000000000
[    0.377248] R13: ffff88016dbaea40 R14: ffffffff822622c0 R15: ffffffff82003fb0
[    0.385348] FS:  0000000000000000(0000) GS:ffff88016d800000(0000) knlGS:0000000000000000
[    0.394533] CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
[    0.401054] CR2: fffffffefce35002 CR3: 000000000300c000 CR4: 00000000003406f0
[    0.409153] DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
[    0.417252] DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
[    0.425350] Stack:
[    0.427638]  ffffffffffffffff ffffffff82256900 ffff88016dbaea40 ffffffff82003f40
[    0.436086]  ffffffff821bbce0 ffffffff82003f88 ffffffff8219c0c2 0000000000000000
[    0.444533]  ffffffff8219ba4a ffffffff822622c0 0000000000083000 00000000ffffffff
[    0.452978] Call Trace:
[    0.455763]  [<ffffffff821bbce0>] efi_late_init+0x9/0xb
[    0.461697]  [<ffffffff8219c0c2>] start_kernel+0x463/0x47f
[    0.467928]  [<ffffffff8219ba4a>] ? set_init_arg+0x55/0x55
[    0.474159]  [<ffffffff8219b120>] ? early_idt_handler_array+0x120/0x120
[    0.481669]  [<ffffffff8219b5ee>] x86_64_start_reservations+0x2a/0x2c
[    0.488982]  [<ffffffff8219b72d>] x86_64_start_kernel+0x13d/0x14c
[    0.495897] Code: 00 41 b4 01 48 8b 78 28 e8 09 36 01 00 48 85 c0 48 89 c3 75 13 48 c7 c7 f8 ac d3 81 31 c0 e8 d7 3b fb fe e9 b5 00 00 00 45 84 e4 <44> 8b 6b 02 74 0d be 06 00 00 00 48 89 df e8 ae 34 0$
[    0.518151] RIP  [<ffffffff821bca49>] efi_bgrt_init+0x144/0x1fd
[    0.524888]  RSP <ffffffff82003f18>
[    0.528851] CR2: fffffffefce35002
[    0.532615] ---[ end trace 7b06521e6ebf2aea ]---
[    0.537852] Kernel panic - not syncing: Attempted to kill the idle task!

As said above one way to fix this bug is to shift %cr3 to efi_pgd but we
are not doing that way because it leaks inner details of how we switch
to EFI page tables into a new call site and it also adds duplicate code.
Instead, we remove the call to efi_lookup_mapped_addr() and always
perform early_mem*() instead of early_io*() because we want to remap RAM
regions and not I/O regions. We also delete efi_lookup_mapped_addr()
because we are no longer using it.

Signed-off-by: Sai Praneeth Prakhya <sai.praneeth.prakhya@intel.com>
Reported-by: Wendy Wang <wendy.wang@intel.com>
Cc: Borislav Petkov <bp@suse.de>
Cc: Josh Triplett <josh@joshtriplett.org>
Cc: Ricardo Neri <ricardo.neri@intel.com>
Cc: Ravi Shankar <ravi.v.shankar@intel.com>
Signed-off-by: Matt Fleming <matt@codeblueprint.co.uk>
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@mfleming
Sai Praneeth authored and mfleming committed Dec 14, 2015
1 parent 26d7f65 commit 50a0cb5
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Showing 2 changed files with 14 additions and 57 deletions.
39 changes: 14 additions & 25 deletions arch/x86/platform/efi/efi-bgrt.c
View file
Original file line number Diff line number Diff line change
Expand Up @@ -31,8 +31,7 @@ struct bmp_header {
void __init efi_bgrt_init(void)
{
acpi_status status;
void __iomem *image;
bool ioremapped = false;
void *image;
struct bmp_header bmp_header;

if (acpi_disabled)
Expand Down Expand Up @@ -73,20 +72,14 @@ void __init efi_bgrt_init(void)
return;
}

image = efi_lookup_mapped_addr(bgrt_tab->image_address);
image = early_memremap(bgrt_tab->image_address, sizeof(bmp_header));
if (!image) {
image = early_ioremap(bgrt_tab->image_address,
sizeof(bmp_header));
ioremapped = true;
if (!image) {
pr_err("Ignoring BGRT: failed to map image header memory\n");
return;
}
pr_err("Ignoring BGRT: failed to map image header memory\n");
return;
}

memcpy_fromio(&bmp_header, image, sizeof(bmp_header));
if (ioremapped)
early_iounmap(image, sizeof(bmp_header));
memcpy(&bmp_header, image, sizeof(bmp_header));
early_memunmap(image, sizeof(bmp_header));
bgrt_image_size = bmp_header.size;

bgrt_image = kmalloc(bgrt_image_size, GFP_KERNEL | __GFP_NOWARN);
Expand All @@ -96,18 +89,14 @@ void __init efi_bgrt_init(void)
return;
}

if (ioremapped) {
image = early_ioremap(bgrt_tab->image_address,
bmp_header.size);
if (!image) {
pr_err("Ignoring BGRT: failed to map image memory\n");
kfree(bgrt_image);
bgrt_image = NULL;
return;
}
image = early_memremap(bgrt_tab->image_address, bmp_header.size);
if (!image) {
pr_err("Ignoring BGRT: failed to map image memory\n");
kfree(bgrt_image);
bgrt_image = NULL;
return;
}

memcpy_fromio(bgrt_image, image, bgrt_image_size);
if (ioremapped)
early_iounmap(image, bmp_header.size);
memcpy(bgrt_image, image, bgrt_image_size);
early_memunmap(image, bmp_header.size);
}
32 changes: 0 additions & 32 deletions drivers/firmware/efi/efi.c
View file
Original file line number Diff line number Diff line change
Expand Up @@ -324,38 +324,6 @@ u64 __init efi_mem_desc_end(efi_memory_desc_t *md)
return end;
}

/*
* We can't ioremap data in EFI boot services RAM, because we've already mapped
* it as RAM. So, look it up in the existing EFI memory map instead. Only
* callable after efi_enter_virtual_mode and before efi_free_boot_services.
*/
void __iomem *efi_lookup_mapped_addr(u64 phys_addr)
{
struct efi_memory_map *map;
void *p;
map = efi.memmap;
if (!map)
return NULL;
if (WARN_ON(!map->map))
return NULL;
for (p = map->map; p < map->map_end; p += map->desc_size) {
efi_memory_desc_t *md = p;
u64 size = md->num_pages << EFI_PAGE_SHIFT;
u64 end = md->phys_addr + size;
if (!(md->attribute & EFI_MEMORY_RUNTIME) &&
md->type != EFI_BOOT_SERVICES_CODE &&
md->type != EFI_BOOT_SERVICES_DATA)
continue;
if (!md->virt_addr)
continue;
if (phys_addr >= md->phys_addr && phys_addr < end) {
phys_addr += md->virt_addr - md->phys_addr;
return (__force void __iomem *)(unsigned long)phys_addr;
}
}
return NULL;
}

static __initdata efi_config_table_type_t common_tables[] = {
{ACPI_20_TABLE_GUID, "ACPI 2.0", &efi.acpi20},
{ACPI_TABLE_GUID, "ACPI", &efi.acpi},
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