[PATCH] x86 efi: bugfix interrupt disabling sequence

[Bart Kuivenhoven]

The problem in efi_main was that the idt was cleared before the
interrupts were disabled.

The UEFI spec states that interrupts aren't used so this shouldn't be
too much of a problem. Peripherals however don't necessarily know about
this and thus might cause interrupts to happen anyway. Even if
ExitBootServices() has been called.

This means there is a risk of an interrupt being triggered while the IDT
register is nullified and the interrupt bit hasn't been cleared,
allowing for a triple fault.

This patch fixes this by clearing the interrupt bit before the lidt
instruction.

Signed-off-by: Bart Kuivenhoven <bemk@xxxxxxxxxx>
---
 arch/x86/boot/compressed/eboot.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/arch/x86/boot/compressed/eboot.c b/arch/x86/boot/compressed/eboot.c
index b7388a4..100b812 100644
--- a/arch/x86/boot/compressed/eboot.c
+++ b/arch/x86/boot/compressed/eboot.c
@@ -1267,11 +1267,11 @@ struct boot_params *efi_main(void *handle, efi_system_table_t *_table,
 	desc->base2 = 0x00;
 #endif /* CONFIG_X86_64 */
 
+	asm volatile("cli");
+
 	asm volatile ("lidt %0" : : "m" (*idt));
 	asm volatile ("lgdt %0" : : "m" (*gdt));
 
-	asm volatile("cli");
-
 	return boot_params;
 fail:
 	return NULL;
-- 
1.8.4

--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@xxxxxxxxxxxxxxx
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/