Merge branch 'x86-urgent-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip

Pull x86 fixes from Thomas Gleixner:
 "A series of fixes for X86:

   - The final fix for the end-of-stack issue in the unwinder
   - Handle non PAT systems gracefully
   - Prevent access to uninitiliazed memory
   - Move early delay calaibration after basic init
   - Fix Kconfig help text
   - Fix a cross compile issue
   - Unbreak older make versions"

* 'x86-urgent-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip:
  x86/timers: Move simple_udelay_calibration past init_hypervisor_platform
  x86/alternatives: Prevent uninitialized stack byte read in apply_alternatives()
  x86/PAT: Fix Xorg regression on CPUs that don't support PAT
  x86/watchdog: Fix Kconfig help text file path reference to lockup watchdog documentation
  x86/build: Permit building with old make versions
  x86/unwind: Add end-of-stack check for ftrace handlers
  Revert "x86/entry: Fix the end of the stack for newly forked tasks"
  x86/boot: Use CROSS_COMPILE prefix for readelf

3 files changed, 49 insertions, 13 deletions

diff --git a/arch/x86/kernel/alternative.c b/arch/x86/kernel/alternative.c
index c5b8f760473c..32e14d137416 100644
--- a/arch/x86/kernel/alternative.c
+++ b/arch/x86/kernel/alternative.c
@@ -409,8 +409,13 @@ void __init_or_module noinline apply_alternatives(struct alt_instr *start,
 		memcpy(insnbuf, replacement, a->replacementlen);
 		insnbuf_sz = a->replacementlen;
 
-		/* 0xe8 is a relative jump; fix the offset. */
-		if (*insnbuf == 0xe8 && a->replacementlen == 5) {
+		/*
+		 * 0xe8 is a relative jump; fix the offset.
+		 *
+		 * Instruction length is checked before the opcode to avoid
+		 * accessing uninitialized bytes for zero-length replacements.
+		 */
+		if (a->replacementlen == 5 && *insnbuf == 0xe8) {
 			*(s32 *)(insnbuf + 1) += replacement - instr;
 			DPRINTK("Fix CALL offset: 0x%x, CALL 0x%lx",
 				*(s32 *)(insnbuf + 1),
diff --git a/arch/x86/kernel/setup.c b/arch/x86/kernel/setup.c
index 0b4d3c686b1e..f81823695014 100644
--- a/arch/x86/kernel/setup.c
+++ b/arch/x86/kernel/setup.c
@@ -980,8 +980,6 @@ void __init setup_arch(char **cmdline_p)
 	 */
 	x86_configure_nx();
 
-	simple_udelay_calibration();
-
 	parse_early_param();
 
 #ifdef CONFIG_MEMORY_HOTPLUG
@@ -1041,6 +1039,8 @@ void __init setup_arch(char **cmdline_p)
 	 */
 	init_hypervisor_platform();
 
+	simple_udelay_calibration();
+
 	x86_init.resources.probe_roms();
 
 	/* after parse_early_param, so could debug it */
diff --git a/arch/x86/kernel/unwind_frame.c b/arch/x86/kernel/unwind_frame.c
index 82c6d7f1fd73..b9389d72b2f7 100644
--- a/arch/x86/kernel/unwind_frame.c
+++ b/arch/x86/kernel/unwind_frame.c
@@ -104,6 +104,11 @@ static inline unsigned long *last_frame(struct unwind_state *state)
 	return (unsigned long *)task_pt_regs(state->task) - 2;
 }
 
+static bool is_last_frame(struct unwind_state *state)
+{
+	return state->bp == last_frame(state);
+}
+
 #ifdef CONFIG_X86_32
 #define GCC_REALIGN_WORDS 3
 #else
@@ -115,16 +120,15 @@ static inline unsigned long *last_aligned_frame(struct unwind_state *state)
 	return last_frame(state) - GCC_REALIGN_WORDS;
 }
 
-static bool is_last_task_frame(struct unwind_state *state)
+static bool is_last_aligned_frame(struct unwind_state *state)
 {
 	unsigned long *last_bp = last_frame(state);
 	unsigned long *aligned_bp = last_aligned_frame(state);
 
 	/*
-	 * We have to check for the last task frame at two different locations
-	 * because gcc can occasionally decide to realign the stack pointer and
-	 * change the offset of the stack frame in the prologue of a function
-	 * called by head/entry code.  Examples:
+	 * GCC can occasionally decide to realign the stack pointer and change
+	 * the offset of the stack frame in the prologue of a function called
+	 * by head/entry code.  Examples:
 	 *
 	 * <start_secondary>:
 	 *      push   %edi
@@ -141,11 +145,38 @@ static bool is_last_task_frame(struct unwind_state *state)
 	 *      push   %rbp
 	 *      mov    %rsp,%rbp
 	 *
-	 * Note that after aligning the stack, it pushes a duplicate copy of
-	 * the return address before pushing the frame pointer.
+	 * After aligning the stack, it pushes a duplicate copy of the return
+	 * address before pushing the frame pointer.
+	 */
+	return (state->bp == aligned_bp && *(aligned_bp + 1) == *(last_bp + 1));
+}
+
+static bool is_last_ftrace_frame(struct unwind_state *state)
+{
+	unsigned long *last_bp = last_frame(state);
+	unsigned long *last_ftrace_bp = last_bp - 3;
+
+	/*
+	 * When unwinding from an ftrace handler of a function called by entry
+	 * code, the stack layout of the last frame is:
+	 *
+	 *   bp
+	 *   parent ret addr
+	 *   bp
+	 *   function ret addr
+	 *   parent ret addr
+	 *   pt_regs
+	 *   -----------------
 	 */
-	return (state->bp == last_bp ||
-		(state->bp == aligned_bp && *(aligned_bp+1) == *(last_bp+1)));
+	return (state->bp == last_ftrace_bp &&
+		*state->bp == *(state->bp + 2) &&
+		*(state->bp + 1) == *(state->bp + 4));
+}
+
+static bool is_last_task_frame(struct unwind_state *state)
+{
+	return is_last_frame(state) || is_last_aligned_frame(state) ||
+	       is_last_ftrace_frame(state);
 }
 
 /*