The patch titled
Subject: kasan: add functions to clear stack poison
has been added to the -mm tree. Its filename is
kasan-add-functions-to-clear-stack-poison.patch
This patch should soon appear at
http://ozlabs.org/~akpm/mmots/broken-out/kasan-add-functions-to-clear-stack-poison.patch
and later at
http://ozlabs.org/~akpm/mmotm/broken-out/kasan-add-functions-to-clear-stack-poison.patch
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------------------------------------------------------
From: Mark Rutland <mark.rutland@xxxxxxx>
Subject: kasan: add functions to clear stack poison
Functions which the compiler has instrumented for ASAN place poison on the
stack shadow upon entry and remove this poison prior to returning.
In some cases (e.g. hotplug and idle), CPUs may exit the kernel a number
of levels deep in C code. If there are any instrumented functions on this
critical path, these will leave portions of the idle thread stack shadow
poisoned.
If a CPU returns to the kernel via a different path (e.g. a cold entry),
then depending on stack frame layout subsequent calls to instrumented
functions may use regions of the stack with stale poison, resulting in
(spurious) KASAN splats to the console.
Contemporary GCCs always add stack shadow poisoning when ASAN is enabled,
even when asked to not instrument a function [1], so we can't simply
annotate functions on the critical path to avoid poisoning.
Instead, this series explicitly removes any stale poison before it can be
hit. In the common hotplug case we clear the entire stack shadow in
common code, before a CPU is brought online.
On architectures which perform a cold return as part of cpu idle may
retain an architecture-specific amount of stack contents. To retain the
poison for this retained context, the arch code must call the core KASAN
code, passing a "watermark" stack pointer value beyond which shadow will
be cleared. Architectures which don't perform a cold return as part of
idle do not need any additional code.
This patch (of 3):
Functions which the compiler has instrumented for KASAN place poison on
the stack shadow upon entry and remove this poision prior to returning.
In some cases (e.g. hotplug and idle), CPUs may exit the kernel a number
of levels deep in C code. If there are any instrumented functions on this
critical path, these will leave portions of the stack shadow poisoned.
If a CPU returns to the kernel via a different path (e.g. a cold entry),
then depending on stack frame layout subsequent calls to instrumented
functions may use regions of the stack with stale poison, resulting in
(spurious) KASAN splats to the console.
To avoid this, we must clear stale poison from the stack prior to
instrumented functions being called. This patch adds functions to the
KASAN core for removing poison from (portions of) a task's stack. These
will be used by subsequent patches to avoid problems with hotplug and
idle.
Signed-off-by: Mark Rutland <mark.rutland@xxxxxxx>
Acked-by: Catalin Marinas <catalin.marinas@xxxxxxx>
Reviewed-by: Andrey Ryabinin <aryabinin@xxxxxxxxxxxxx>
Cc: Alexander Potapenko <glider@xxxxxxxxxx>
Cc: Lorenzo Pieralisi <lorenzo.pieralisi@xxxxxxx>
Cc: Will Deacon <will.deacon@xxxxxxx>
Cc: Ingo Molnar <mingo@xxxxxxxxxx>
Cc: Peter Zijlstra <peterz@xxxxxxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---
include/linux/kasan.h | 6 +++++-
mm/kasan/kasan.c | 20 ++++++++++++++++++++
2 files changed, 25 insertions(+), 1 deletion(-)
diff -puN include/linux/kasan.h~kasan-add-functions-to-clear-stack-poison include/linux/kasan.h
--- a/include/linux/kasan.h~kasan-add-functions-to-clear-stack-poison
+++ a/include/linux/kasan.h
@@ -1,6 +1,7 @@
#ifndef _LINUX_KASAN_H
#define _LINUX_KASAN_H
+#include <linux/sched.h>
#include <linux/types.h>
struct kmem_cache;
@@ -13,7 +14,6 @@ struct vm_struct;
#include <asm/kasan.h>
#include <asm/pgtable.h>
-#include <linux/sched.h>
extern unsigned char kasan_zero_page[PAGE_SIZE];
extern pte_t kasan_zero_pte[PTRS_PER_PTE];
@@ -43,6 +43,8 @@ static inline void kasan_disable_current
void kasan_unpoison_shadow(const void *address, size_t size);
+void kasan_unpoison_task_stack(struct task_struct *task);
+
void kasan_alloc_pages(struct page *page, unsigned int order);
void kasan_free_pages(struct page *page, unsigned int order);
@@ -66,6 +68,8 @@ void kasan_free_shadow(const struct vm_s
static inline void kasan_unpoison_shadow(const void *address, size_t size) {}
+static inline void kasan_unpoison_task_stack(struct task_struct *task) {}
+
static inline void kasan_enable_current(void) {}
static inline void kasan_disable_current(void) {}
diff -puN mm/kasan/kasan.c~kasan-add-functions-to-clear-stack-poison mm/kasan/kasan.c
--- a/mm/kasan/kasan.c~kasan-add-functions-to-clear-stack-poison
+++ a/mm/kasan/kasan.c
@@ -20,6 +20,7 @@
#include <linux/init.h>
#include <linux/kernel.h>
#include <linux/kmemleak.h>
+#include <linux/linkage.h>
#include <linux/memblock.h>
#include <linux/memory.h>
#include <linux/mm.h>
@@ -60,6 +61,25 @@ void kasan_unpoison_shadow(const void *a
}
}
+static void __kasan_unpoison_stack(struct task_struct *task, void *sp)
+{
+ void *base = task_stack_page(task);
+ size_t size = sp - base;
+
+ kasan_unpoison_shadow(base, size);
+}
+
+/* Unpoison the entire stack for a task. */
+void kasan_unpoison_task_stack(struct task_struct *task)
+{
+ __kasan_unpoison_stack(task, task_stack_page(task) + THREAD_SIZE);
+}
+
+/* Unpoison the stack for the current task beyond a watermark sp value. */
+asmlinkage void kasan_unpoison_remaining_stack(void *sp)
+{
+ __kasan_unpoison_stack(current, sp);
+}
/*
* All functions below always inlined so compiler could
_
Patches currently in -mm which might be from mark.rutland@xxxxxxx are
kasan-add-functions-to-clear-stack-poison.patch
sched-kasan-remove-stale-kasan-poison-after-hotplug.patch
arm64-kasan-clear-stale-stack-poison.patch
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