This is a note to let you know that I've just added the patch titled

x86/dumpstack: Fix partial register dumps

to the 4.14-stable tree which can be found at: http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git%3Ba=su...

The filename of the patch is: x86-dumpstack-fix-partial-register-dumps.patch and it can be found in the queue-4.14 subdirectory.

If you, or anyone else, feels it should not be added to the stable tree, please let stable@vger.kernel.org know about it.

From a9cdbe72c4e8bf3b38781c317a79326e2e1a230d Mon Sep 17 00:00:00 2001

From: Josh Poimboeuf jpoimboe@redhat.com Date: Sun, 31 Dec 2017 10:18:06 -0600 Subject: x86/dumpstack: Fix partial register dumps MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit

From: Josh Poimboeuf jpoimboe@redhat.com

commit a9cdbe72c4e8bf3b38781c317a79326e2e1a230d upstream.

The show_regs_safe() logic is wrong. When there's an iret stack frame, it prints the entire pt_regs -- most of which is random stack data -- instead of just the five registers at the end.

show_regs_safe() is also poorly named: the on_stack() checks aren't for safety. Rename the function to show_regs_if_on_stack() and add a comment to explain why the checks are needed.

These issues were introduced with the "partial register dump" feature of the following commit:

b02fcf9ba121 ("x86/unwinder: Handle stack overflows more gracefully")

That patch had gone through a few iterations of development, and the above issues were artifacts from a previous iteration of the patch where 'regs' pointed directly to the iret frame rather than to the (partially empty) pt_regs.

Tested-by: Alexander Tsoy alexander@tsoy.me Signed-off-by: Josh Poimboeuf jpoimboe@redhat.com Cc: Andy Lutomirski luto@kernel.org Cc: Linus Torvalds torvalds@linux-foundation.org Cc: Peter Zijlstra peterz@infradead.org Cc: Thomas Gleixner tglx@linutronix.de Cc: Toralf Förster toralf.foerster@gmx.de Fixes: b02fcf9ba121 ("x86/unwinder: Handle stack overflows more gracefully") Link: http://lkml.kernel.org/r/5b05b8b344f59db2d3d50dbdeba92d60f2304c54.1514736742... Signed-off-by: Ingo Molnar mingo@kernel.org Signed-off-by: Greg Kroah-Hartman gregkh@linuxfoundation.org

--- arch/x86/include/asm/unwind.h | 17 +++++++++++++---- arch/x86/kernel/dumpstack.c | 28 ++++++++++++++++++++-------- arch/x86/kernel/stacktrace.c | 2 +- 3 files changed, 34 insertions(+), 13 deletions(-)

--- a/arch/x86/include/asm/unwind.h +++ b/arch/x86/include/asm/unwind.h @@ -56,18 +56,27 @@ void unwind_start(struct unwind_state *s

#if defined(CONFIG_UNWINDER_ORC) || defined(CONFIG_UNWINDER_FRAME_POINTER) /* - * WARNING: The entire pt_regs may not be safe to dereference. In some cases, - * only the iret frame registers are accessible. Use with caution! + * If 'partial' returns true, only the iret frame registers are valid. */ -static inline struct pt_regs *unwind_get_entry_regs(struct unwind_state *state) +static inline struct pt_regs *unwind_get_entry_regs(struct unwind_state *state, + bool *partial) { if (unwind_done(state)) return NULL;

+ if (partial) { +#ifdef CONFIG_UNWINDER_ORC + *partial = !state->full_regs; +#else + *partial = false; +#endif + } + return state->regs; } #else -static inline struct pt_regs *unwind_get_entry_regs(struct unwind_state *state) +static inline struct pt_regs *unwind_get_entry_regs(struct unwind_state *state, + bool *partial) { return NULL; } --- a/arch/x86/kernel/dumpstack.c +++ b/arch/x86/kernel/dumpstack.c @@ -76,12 +76,23 @@ void show_iret_regs(struct pt_regs *regs regs->sp, regs->flags); }

-static void show_regs_safe(struct stack_info *info, struct pt_regs *regs) +static void show_regs_if_on_stack(struct stack_info *info, struct pt_regs *regs, + bool partial) { - if (on_stack(info, regs, sizeof(*regs))) + /* + * These on_stack() checks aren't strictly necessary: the unwind code + * has already validated the 'regs' pointer. The checks are done for + * ordering reasons: if the registers are on the next stack, we don't + * want to print them out yet. Otherwise they'll be shown as part of + * the wrong stack. Later, when show_trace_log_lvl() switches to the + * next stack, this function will be called again with the same regs so + * they can be printed in the right context. + */ + if (!partial && on_stack(info, regs, sizeof(*regs))) { __show_regs(regs, 0); - else if (on_stack(info, (void *)regs + IRET_FRAME_OFFSET, - IRET_FRAME_SIZE)) { + + } else if (partial && on_stack(info, (void *)regs + IRET_FRAME_OFFSET, + IRET_FRAME_SIZE)) { /* * When an interrupt or exception occurs in entry code, the * full pt_regs might not have been saved yet. In that case @@ -98,6 +109,7 @@ void show_trace_log_lvl(struct task_stru struct stack_info stack_info = {0}; unsigned long visit_mask = 0; int graph_idx = 0; + bool partial;

printk("%sCall Trace:\n", log_lvl);

@@ -140,7 +152,7 @@ void show_trace_log_lvl(struct task_stru printk("%s <%s>\n", log_lvl, stack_name);

if (regs) - show_regs_safe(&stack_info, regs); + show_regs_if_on_stack(&stack_info, regs, partial);

/* * Scan the stack, printing any text addresses we find. At the @@ -164,7 +176,7 @@ void show_trace_log_lvl(struct task_stru

/* * Don't print regs->ip again if it was already printed - * by show_regs_safe() below. + * by show_regs_if_on_stack(). */ if (regs && stack == &regs->ip) goto next; @@ -199,9 +211,9 @@ next: unwind_next_frame(&state);

/* if the frame has entry regs, print them */ - regs = unwind_get_entry_regs(&state); + regs = unwind_get_entry_regs(&state, &partial); if (regs) - show_regs_safe(&stack_info, regs); + show_regs_if_on_stack(&stack_info, regs, partial); }

if (stack_name) --- a/arch/x86/kernel/stacktrace.c +++ b/arch/x86/kernel/stacktrace.c @@ -98,7 +98,7 @@ static int __save_stack_trace_reliable(s for (unwind_start(&state, task, NULL, NULL); !unwind_done(&state); unwind_next_frame(&state)) {

- regs = unwind_get_entry_regs(&state); + regs = unwind_get_entry_regs(&state, NULL); if (regs) { /* * Kernel mode registers on the stack indicate an

Patches currently in stable-queue which might be from jpoimboe@redhat.com are

queue-4.14/x86-dumpstack-print-registers-for-first-stack-frame.patch queue-4.14/x86-process-define-cpu_tss_rw-in-same-section-as-declaration.patch queue-4.14/x86-dumpstack-fix-partial-register-dumps.patch