linux-kernel - [PATCH v3 6/7] x86: Fix thread_saved

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Date:	Sat, 13 Aug 2016 12:38:21 -0400
From:	Brian Gerst <brgerst@...il.com>
To:	x86@...nel.org, linux-kernel@...r.kernel.org
Cc:	Ingo Molnar <mingo@...nel.org>, "H. Peter Anvin" <hpa@...or.com>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Denys Vlasenko <dvlasenk@...hat.com>,
	Andy Lutomirski <luto@...capital.net>,
	Borislav Petkov <bp@...e.de>,
	Thomas Gleixner <tglx@...utronix.de>,
	Josh Poimboeuf <jpoimboe@...hat.com>
Subject: [PATCH v3 6/7] x86: Fix thread_saved_pc()

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@...il.com>
---
 arch/x86/include/asm/processor.h | 10 ++--------
 arch/x86/kernel/process.c        | 11 +++++++++++
 arch/x86/kernel/process_32.c     |  8 --------
 3 files changed, 13 insertions(+), 16 deletions(-)

diff --git a/arch/x86/include/asm/processor.h b/arch/x86/include/asm/processor.h
index 6fee863..b22fb5a 100644
--- a/arch/x86/include/asm/processor.h
+++ b/arch/x86/include/asm/processor.h
@@ -721,8 +721,6 @@ static inline void spin_lock_prefetch(const void *x)
 	.addr_limit		= KERNEL_DS,				  \
 }
 
-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"
@@ -773,17 +771,13 @@ extern unsigned long thread_saved_pc(struct task_struct *tsk);
 	.addr_limit		= KERNEL_DS,			\
 }
 
-/*
- * 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 0115a4a..c1fa790 100644
--- a/arch/x86/kernel/process.c
+++ b/arch/x86/kernel/process.c
@@ -514,6 +514,17 @@ unsigned long arch_randomize_brk(struct mm_struct *mm)
 }
 
 /*
+ * Return saved PC of a blocked thread.
+ * What is this good for? it will be always the scheduler or ret_from_fork.
+ */
+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 18714a1..404efdf 100644
--- a/arch/x86/kernel/process_32.c
+++ b/arch/x86/kernel/process_32.c
@@ -55,14 +55,6 @@
 #include <asm/switch_to.h>
 #include <asm/vm86.h>
 
-/*
- * 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