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| author |   Joerg Roedel <jroedel@suse.de> | 2018-08-31 10:05:38 +0200 |
|---|---|---|
| committer |   Thomas Gleixner <tglx@linutronix.de> | 2018-08-31 17:45:54 +0200 |
| commit | eeb89e2bb1ac45b0836d4170e97a988c3a746c62 (patch) | |
| tree | 4bbdbe94fac1d57965293198cb345324d4b89a1d /arch | |
| parent | x86/nmi: Fix NMI uaccess race against CR3 switching (diff) | |
| download | linux-dev-eeb89e2bb1ac45b0836d4170e97a988c3a746c62.tar.xz linux-dev-eeb89e2bb1ac45b0836d4170e97a988c3a746c62.zip | |
x86/efi: Load fixmap GDT in efi_call_phys_epilog()
When PTI is enabled on x86-32 the kernel uses the GDT mapped in the fixmap
for the simple reason that this address is also mapped for user-space.
The efi_call_phys_prolog()/efi_call_phys_epilog() wrappers change the GDT
to call EFI runtime services and switch back to the kernel GDT when they
return. But the switch-back uses the writable GDT, not the fixmap GDT.
When that happened and and the CPU returns to user-space it switches to the
user %cr3 and tries to restore user segment registers. This fails because
the writable GDT is not mapped in the user page-table, and without a GDT
the fault handlers also can't be launched. The result is a triple fault and
reboot of the machine.
Fix that by restoring the GDT back to the fixmap GDT which is also mapped
in the user page-table.
Fixes: 7757d607c6b3 x86/pti: ('Allow CONFIG_PAGE_TABLE_ISOLATION for x86_32')
Reported-by: Guenter Roeck <linux@roeck-us.net>
Signed-off-by: Joerg Roedel <jroedel@suse.de>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Tested-by: Guenter Roeck <linux@roeck-us.net>
Cc: Ard Biesheuvel <ard.biesheuvel@linaro.org>
Cc: Michal Hocko <mhocko@suse.com>
Cc: Andi Kleen <ak@linux.intel.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Dave Hansen <dave.hansen@intel.com>
Cc: Pavel Machek <pavel@ucw.cz>
Cc: hpa@zytor.com
Cc: linux-efi@vger.kernel.org
Link: https://lkml.kernel.org/r/1535702738-10971-1-git-send-email-joro@8bytes.org
Diffstat (limited to 'arch')
| -rw-r--r-- | arch/x86/platform/efi/efi_32.c | 8 |
1 files changed, 2 insertions, 6 deletions
diff --git a/arch/x86/platform/efi/efi_32.c b/arch/x86/platform/efi/efi_32.c index 324b93328b37..05ca14222463 100644 --- a/arch/x86/platform/efi/efi_32.c +++ b/arch/x86/platform/efi/efi_32.c @@ -85,14 +85,10 @@ pgd_t * __init efi_call_phys_prolog(void) void __init efi_call_phys_epilog(pgd_t *save_pgd) { - struct desc_ptr gdt_descr; - - gdt_descr.address = (unsigned long)get_cpu_gdt_rw(0); - gdt_descr.size = GDT_SIZE - 1; - load_gdt(&gdt_descr); - load_cr3(save_pgd); __flush_tlb_all(); + + load_fixmap_gdt(0); } void __init efi_runtime_update_mappings(void) |