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Commit e7a2ff59 authored by Zachary Amsden's avatar Zachary Amsden Committed by Linus Torvalds
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[PATCH] i386: load_tls() fix 



Subtle fix: load_TLS has been moved after saving %fs and %gs segments to avoid
creating non-reversible segments.  This could conceivably cause a bug if the
kernel ever needed to save and restore fs/gs from the NMI handler.  It
currently does not, but this is the safest approach to avoiding fs/gs
corruption.  SMIs are safe, since SMI saves the descriptor hidden state.

Signed-off-by: default avatarZachary Amsden <zach@vmware.com>
Signed-off-by: default avatarAndrew Morton <akpm@osdl.org>
Signed-off-by: default avatarLinus Torvalds <torvalds@osdl.org>
parent 2f2984eb

arch/i386/kernel/process.c

+12 −7
Original line number Original line Diff line number Diff line
@@ -678,21 +678,26 @@ struct task_struct fastcall * __switch_to(struct task_struct *prev_p, struct tas 
	__unlazy_fpu(prev_p);

	__unlazy_fpu(prev_p);





	/*

	/*

	 * Reload esp0, LDT and the page table pointer:

	 * Reload esp0.

	 */

	 */

	load_esp0(tss, next);

	load_esp0(tss, next);





	/*

	/*

	 * Load the per-thread Thread-Local Storage descriptor.

	 * Save away %fs and %gs. No need to save %es and %ds, as

	 * those are always kernel segments while inside the kernel.

	 * Doing this before setting the new TLS descriptors avoids

	 * the situation where we temporarily have non-reloadable

	 * segments in %fs and %gs.  This could be an issue if the

	 * NMI handler ever used %fs or %gs (it does not today), or

	 * if the kernel is running inside of a hypervisor layer.

	 */

	 */

	load_TLS(next, cpu);

	savesegment(fs, prev->fs);

	savesegment(gs, prev->gs);





	/*

	/*

	 * Save away %fs and %gs. No need to save %es and %ds, as

	 * Load the per-thread Thread-Local Storage descriptor.

	 * those are always kernel segments while inside the kernel.

	 */

	 */

	asm volatile("mov %%fs,%0":"=m" (prev->fs));

	load_TLS(next, cpu);

	asm volatile("mov %%gs,%0":"=m" (prev->gs));





	/*

	/*

	 * Restore %fs and %gs if needed.

	 * Restore %fs and %gs if needed.