x86/stackframe/32: Provide consistent pt_regs

Currently pt_regs on x86_32 has an oddity in that kernel regs
(!user_mode(regs)) are short two entries (esp/ss). This means that any
code trying to use them (typically: regs->sp) needs to jump through
some unfortunate hoops.

Change the entry code to fix this up and create a full pt_regs frame.

This then simplifies various trampolines in ftrace and kprobes, the
stack unwinder, ptrace, kdump and kgdb.

Much thanks to Josh for help with the cleanups!

Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Reviewed-by: Josh Poimboeuf <jpoimboe@redhat.com>
Acked-by: Masami Hiramatsu <mhiramat@kernel.org>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Ingo Molnar <mingo@kernel.org>

3 files changed, 3 insertions, 33 deletions

diff --git a/arch/x86/include/asm/kexec.h b/arch/x86/include/asm/kexec.h
index 003f2daa3b0f..5e7d6b46de97 100644
--- a/arch/x86/include/asm/kexec.h
+++ b/arch/x86/include/asm/kexec.h
@@ -71,22 +71,6 @@ struct kimage;
 #define KEXEC_BACKUP_SRC_END	(640 * 1024UL - 1)	/* 640K */
 
 /*
- * CPU does not save ss and sp on stack if execution is already
- * running in kernel mode at the time of NMI occurrence. This code
- * fixes it.
- */
-static inline void crash_fixup_ss_esp(struct pt_regs *newregs,
-				      struct pt_regs *oldregs)
-{
-#ifdef CONFIG_X86_32
-	newregs->sp = (unsigned long)&(oldregs->sp);
-	asm volatile("xorl %%eax, %%eax\n\t"
-		     "movw %%ss, %%ax\n\t"
-		     :"=a"(newregs->ss));
-#endif
-}
-
-/*
  * This function is responsible for capturing register states if coming
  * via panic otherwise just fix up the ss and sp if coming via kernel
  * mode exception.
@@ -96,7 +80,6 @@ static inline void crash_setup_regs(struct pt_regs *newregs,
 {
 	if (oldregs) {
 		memcpy(newregs, oldregs, sizeof(*newregs));
-		crash_fixup_ss_esp(newregs, oldregs);
 	} else {
 #ifdef CONFIG_X86_32
 		asm volatile("movl %%ebx,%0" : "=m"(newregs->bx));
diff --git a/arch/x86/include/asm/ptrace.h b/arch/x86/include/asm/ptrace.h
index 8a7fc0cca2d1..3703c91f441e 100644
--- a/arch/x86/include/asm/ptrace.h
+++ b/arch/x86/include/asm/ptrace.h
@@ -166,14 +166,10 @@ static inline bool user_64bit_mode(struct pt_regs *regs)
 #define compat_user_stack_pointer()	current_pt_regs()->sp
 #endif
 
-#ifdef CONFIG_X86_32
-extern unsigned long kernel_stack_pointer(struct pt_regs *regs);
-#else
 static inline unsigned long kernel_stack_pointer(struct pt_regs *regs)
 {
 	return regs->sp;
 }
-#endif
 
 #define GET_IP(regs) ((regs)->ip)
 #define GET_FP(regs) ((regs)->bp)
@@ -201,14 +197,6 @@ static inline unsigned long regs_get_register(struct pt_regs *regs,
 	if (unlikely(offset > MAX_REG_OFFSET))
 		return 0;
 #ifdef CONFIG_X86_32
-	/*
-	 * Traps from the kernel do not save sp and ss.
-	 * Use the helper function to retrieve sp.
-	 */
-	if (offset == offsetof(struct pt_regs, sp) &&
-	    regs->cs == __KERNEL_CS)
-		return kernel_stack_pointer(regs);
-
 	/* The selector fields are 16-bit. */
 	if (offset == offsetof(struct pt_regs, cs) ||
 	    offset == offsetof(struct pt_regs, ss) ||
@@ -234,8 +222,7 @@ static inline unsigned long regs_get_register(struct pt_regs *regs,
 static inline int regs_within_kernel_stack(struct pt_regs *regs,
 					   unsigned long addr)
 {
-	return ((addr & ~(THREAD_SIZE - 1))  ==
-		(kernel_stack_pointer(regs) & ~(THREAD_SIZE - 1)));
+	return ((addr & ~(THREAD_SIZE - 1)) == (regs->sp & ~(THREAD_SIZE - 1)));
 }
 
 /**
@@ -249,7 +236,7 @@ static inline int regs_within_kernel_stack(struct pt_regs *regs,
  */
 static inline unsigned long *regs_get_kernel_stack_nth_addr(struct pt_regs *regs, unsigned int n)
 {
-	unsigned long *addr = (unsigned long *)kernel_stack_pointer(regs);
+	unsigned long *addr = (unsigned long *)regs->sp;
 
 	addr += n;
 	if (regs_within_kernel_stack(regs, (unsigned long)addr))
diff --git a/arch/x86/include/asm/stacktrace.h b/arch/x86/include/asm/stacktrace.h
index a8d0cdf48616..14db05086bbf 100644
--- a/arch/x86/include/asm/stacktrace.h
+++ b/arch/x86/include/asm/stacktrace.h
@@ -78,7 +78,7 @@ static inline unsigned long *
 get_stack_pointer(struct task_struct *task, struct pt_regs *regs)
 {
 	if (regs)
-		return (unsigned long *)kernel_stack_pointer(regs);
+		return (unsigned long *)regs->sp;
 
 	if (task == current)
 		return __builtin_frame_address(0);