[PATCH] x86: fix range check in tlbflush debugfs interface

[Jan Beulich]

Since the shift count settable there is used for shifting values of
type "unsigned long", its value must not match or exceed BITS_PER_LONG
(otherwise the shift operations are undefined). Similarly, the value
must not be negative (but -1 must be permitted, as that's the value
used to distinguish the case of the fine grained flushing being
disabled).

Signed-off-by: Jan Beulich <jbeulich@xxxxxxxx>
Cc: Alex Shi <alex.shi@xxxxxxxxx>

---
 arch/x86/mm/tlb.c |    2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

--- 3.6-rc4/arch/x86/mm/tlb.c
+++ 3.6-rc4-x86-tlb_flushall_shift-limits/arch/x86/mm/tlb.c
@@ -320,7 +320,7 @@ static ssize_t tlbflush_write_file(struc
 	if (kstrtos8(buf, 0, &shift))
 		return -EINVAL;
 
-	if (shift > 64)
+	if (shift < -1 || shift >= BITS_PER_LONG)
 		return -EINVAL;
 
 	tlb_flushall_shift = shift;



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