eeb89e2bb1
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:
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|---|---|---|
| .. | ||
| Makefile | ||
| early_printk.c | ||
| efi.c | ||
| efi_32.c | ||
| efi_64.c | ||
| efi_stub_32.S | ||
| efi_stub_64.S | ||
| efi_thunk_64.S | ||
| quirks.c | ||