[PATCH v2 6/6] x86: Fix thread_saved_pc()

Brian Gerst
2016-06-18T20:56:54Z

thread_saved_pc() was using a completely bogus method to get the return
address. Since switch_to() was previously inlined, there was no sane way
to know where on the stack the return address was stored. Now with the
frame of a sleeping thread well defined, this can be implemented correctly.

Signed-off-by: Brian Gerst <brgerst@gmail.com>
---
arch/x86/include/asm/processor.h | 10 ++--------
arch/x86/kernel/process.c | 10 ++++++++++
arch/x86/kernel/process_32.c | 8 --------
3 files changed, 12 insertions(+), 16 deletions(-)

diff --git a/arch/x86/include/asm/processor.h b/arch/x86/include/asm/processor.h
index 1e7d634..413f4f1 100644
--- a/arch/x86/include/asm/processor.h
+++ b/arch/x86/include/asm/processor.h
@@ -716,8 +716,6 @@ static inline void spin_lock_prefetch(const void *x)
.io_bitmap_ptr = NULL, \
}

-extern unsigned long thread_saved_pc(struct task_struct *tsk);
-
/*
* TOP_OF_KERNEL_STACK_PADDING reserves 8 bytes on top of the ring0 stack.
* This is necessary to guarantee that the entire "struct pt_regs"
@@ -767,17 +765,13 @@ extern unsigned long thread_saved_pc(struct task_struct *tsk);
.sp0 = TOP_OF_INIT_STACK \
}

-/*
- * Return saved PC of a blocked thread.
- * What is this good for? it will be always the scheduler or ret_from_fork.
- */
-#define thread_saved_pc(t) READ_ONCE_NOCHECK(*(unsigned long *)((t)->thread.sp - 8))
-
#define task_pt_regs(tsk) ((struct pt_regs *)(tsk)->thread.sp0 - 1)
extern unsigned long KSTK_ESP(struct task_struct *task);

#endif /* CONFIG_X86_64 */

+extern unsigned long thread_saved_pc(struct task_struct *tsk);
+
extern void start_thread(struct pt_regs *regs, unsigned long new_ip,
unsigned long new_sp);

diff --git a/arch/x86/kernel/process.c b/arch/x86/kernel/process.c
index 00ebab0..db458c4 100644
--- a/arch/x86/kernel/process.c
+++ b/arch/x86/kernel/process.c
@@ -513,6 +513,16 @@ unsigned long arch_randomize_brk(struct mm_struct *mm)
}

/*
+ * Return saved PC of a blocked thread.
+ */
+unsigned long thread_saved_pc(struct task_struct *tsk)
+{
+ struct inactive_task_frame *frame =
+ (struct inactive_task_frame *) READ_ONCE(tsk->thread.sp);
+ return READ_ONCE_NOCHECK(frame->ret_addr);
+}
+
+/*
* Called from fs/proc with a reference on @p to find the function
* which called into schedule(). This needs to be done carefully
* because the task might wake up and we might look at a stack
diff --git a/arch/x86/kernel/process_32.c b/arch/x86/kernel/process_32.c
index acee6ca..bcf0a38 100644
--- a/arch/x86/kernel/process_32.c
+++ b/arch/x86/kernel/process_32.c
@@ -58,14 +58,6 @@
asmlinkage void ret_from_fork(void) __asm__("ret_from_fork");
asmlinkage void ret_from_kernel_thread(void) __asm__("ret_from_kernel_thread");

-/*
- * Return saved PC of a blocked thread.
- */
-unsigned long thread_saved_pc(struct task_struct *tsk)
-{
- return ((unsigned long *)tsk->thread.sp)[3];
-}
-
void __show_regs(struct pt_regs *regs, int all)
{
unsigned long cr0 = 0L, cr2 = 0L, cr3 = 0L, cr4 = 0L;
--
2.5.5