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-rw-r--r--include/asm-i386/processor.h12
1 files changed, 11 insertions, 1 deletions
diff --git a/include/asm-i386/processor.h b/include/asm-i386/processor.h
index 13ecf66b098..29ad87e9123 100644
--- a/include/asm-i386/processor.h
+++ b/include/asm-i386/processor.h
@@ -561,10 +561,20 @@ unsigned long get_wchan(struct task_struct *p);
(unsigned long)(&__ptr[THREAD_SIZE_LONGS]); \
})
+/*
+ * The below -8 is to reserve 8 bytes on top of the ring0 stack.
+ * This is necessary to guarantee that the entire "struct pt_regs"
+ * is accessable even if the CPU haven't stored the SS/ESP registers
+ * on the stack (interrupt gate does not save these registers
+ * when switching to the same priv ring).
+ * Therefore beware: accessing the xss/esp fields of the
+ * "struct pt_regs" is possible, but they may contain the
+ * completely wrong values.
+ */
#define task_pt_regs(task) \
({ \
struct pt_regs *__regs__; \
- __regs__ = (struct pt_regs *)KSTK_TOP((task)->thread_info); \
+ __regs__ = (struct pt_regs *)(KSTK_TOP((task)->thread_info)-8); \
__regs__ - 1; \
})