diff options
| author | Zachary Amsden <zach@vmware.com> | 2005-09-03 15:56:39 -0700 |
|---|---|---|
| committer | Linus Torvalds <torvalds@evo.osdl.org> | 2005-09-05 00:06:11 -0700 |
| commit | e7a2ff593c0e48b130434dee4d2fd3452a850e6f (patch) | |
| tree | 89bca4c0a0818d1e217c76866f62c1b133a425d7 /arch/i386 | |
| parent | 2f2984eb4afb2a4298e3186cb49cc7e88dd6d929 (diff) | |
[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: Zachary Amsden <zach@vmware.com>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>
Diffstat (limited to 'arch/i386')
| -rw-r--r-- | arch/i386/kernel/process.c | 19 |
1 files changed, 12 insertions, 7 deletions
diff --git a/arch/i386/kernel/process.c b/arch/i386/kernel/process.c index 761d4ed47ef..9d94995e967 100644 --- a/arch/i386/kernel/process.c +++ b/arch/i386/kernel/process.c @@ -678,21 +678,26 @@ struct task_struct fastcall * __switch_to(struct task_struct *prev_p, struct tas __unlazy_fpu(prev_p); /* - * Reload esp0, LDT and the page table pointer: + * Reload esp0. */ 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 - * those are always kernel segments while inside the kernel. + * Load the per-thread Thread-Local Storage descriptor. */ - asm volatile("mov %%fs,%0":"=m" (prev->fs)); - asm volatile("mov %%gs,%0":"=m" (prev->gs)); + load_TLS(next, cpu); /* * Restore %fs and %gs if needed. |