x86/segments/64: When loadsegment(fs, ...) fails, clear the base
On AMD CPUs, a failed loadsegment currently may not clear the FS
base. Fix it.
While we're at it, prevent loadsegment(gs, xyz) from even compiling
on 64-bit kernels. It shouldn't be used.
Signed-off-by: Andy Lutomirski <luto@kernel.org>
Cc: Andy Lutomirski <luto@amacapital.net>
Cc: Borislav Petkov <bp@alien8.de>
Cc: Brian Gerst <brgerst@gmail.com>
Cc: Denys Vlasenko <dvlasenk@redhat.com>
Cc: H. Peter Anvin <hpa@zytor.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Link: http://lkml.kernel.org/r/a084c1b93b7b1408b58d3fd0b5d6e47da8e7d7cf.1461698311.git.luto@kernel.org
Signed-off-by: Ingo Molnar <mingo@kernel.org>
diff --git a/arch/x86/mm/extable.c b/arch/x86/mm/extable.c
index aaeda3f..4bb53b8 100644
--- a/arch/x86/mm/extable.c
+++ b/arch/x86/mm/extable.c
@@ -70,6 +70,16 @@
}
EXPORT_SYMBOL(ex_handler_wrmsr_unsafe);
+bool ex_handler_clear_fs(const struct exception_table_entry *fixup,
+ struct pt_regs *regs, int trapnr)
+{
+ if (static_cpu_has(X86_BUG_NULL_SEG))
+ asm volatile ("mov %0, %%fs" : : "rm" (__USER_DS));
+ asm volatile ("mov %0, %%fs" : : "rm" (0));
+ return ex_handler_default(fixup, regs, trapnr);
+}
+EXPORT_SYMBOL(ex_handler_clear_fs);
+
bool ex_has_fault_handler(unsigned long ip)
{
const struct exception_table_entry *e;