Commit 9f7d416c authored Oct 14, 2016 by Dmitry Vyukov Committed by Ingo Molnar Oct 16, 2016

kprobes: Unpoison stack in jprobe_return() for KASAN



I observed false KSAN positives in the sctp code, when
sctp uses jprobe_return() in jsctp_sf_eat_sack().

The stray 0xf4 in shadow memory are stack redzones:

[     ] ==================================================================
[     ] BUG: KASAN: stack-out-of-bounds in memcmp+0xe9/0x150 at addr ffff88005e48f480
[     ] Read of size 1 by task syz-executor/18535
[     ] page:ffffea00017923c0 count:0 mapcount:0 mapping:          (null) index:0x0
[     ] flags: 0x1fffc0000000000()
[     ] page dumped because: kasan: bad access detected
[     ] CPU: 1 PID: 18535 Comm: syz-executor Not tainted 4.8.0+ #28
[     ] Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
[     ]  ffff88005e48f2d0 ffffffff82d2b849 ffffffff0bc91e90 fffffbfff10971e8
[     ]  ffffed000bc91e90 ffffed000bc91e90 0000000000000001 0000000000000000
[     ]  ffff88005e48f480 ffff88005e48f350 ffffffff817d3169 ffff88005e48f370
[     ] Call Trace:
[     ]  [<ffffffff82d2b849>] dump_stack+0x12e/0x185
[     ]  [<ffffffff817d3169>] kasan_report+0x489/0x4b0
[     ]  [<ffffffff817d31a9>] __asan_report_load1_noabort+0x19/0x20
[     ]  [<ffffffff82d49529>] memcmp+0xe9/0x150
[     ]  [<ffffffff82df7486>] depot_save_stack+0x176/0x5c0
[     ]  [<ffffffff817d2031>] save_stack+0xb1/0xd0
[     ]  [<ffffffff817d27f2>] kasan_slab_free+0x72/0xc0
[     ]  [<ffffffff817d05b8>] kfree+0xc8/0x2a0
[     ]  [<ffffffff85b03f19>] skb_free_head+0x79/0xb0
[     ]  [<ffffffff85b0900a>] skb_release_data+0x37a/0x420
[     ]  [<ffffffff85b090ff>] skb_release_all+0x4f/0x60
[     ]  [<ffffffff85b11348>] consume_skb+0x138/0x370
[     ]  [<ffffffff8676ad7b>] sctp_chunk_put+0xcb/0x180
[     ]  [<ffffffff8676ae88>] sctp_chunk_free+0x58/0x70
[     ]  [<ffffffff8677fa5f>] sctp_inq_pop+0x68f/0xef0
[     ]  [<ffffffff8675ee36>] sctp_assoc_bh_rcv+0xd6/0x4b0
[     ]  [<ffffffff8677f2c1>] sctp_inq_push+0x131/0x190
[     ]  [<ffffffff867bad69>] sctp_backlog_rcv+0xe9/0xa20
[ ... ]
[     ] Memory state around the buggy address:
[     ]  ffff88005e48f380: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
[     ]  ffff88005e48f400: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
[     ] >ffff88005e48f480: f4 f4 00 00 00 00 00 00 00 00 00 00 00 00 00 00
[     ]                    ^
[     ]  ffff88005e48f500: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
[     ]  ffff88005e48f580: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
[     ] ==================================================================

KASAN stack instrumentation poisons stack redzones on function entry
and unpoisons them on function exit. If a function exits abnormally
(e.g. with a longjmp like jprobe_return()), stack redzones are left
poisoned. Later this leads to random KASAN false reports.

Unpoison stack redzones in the frames we are going to jump over
before doing actual longjmp in jprobe_return().

Signed-off-by: Dmitry Vyukov <dvyukov@google.com>
Acked-by: Masami Hiramatsu <mhiramat@kernel.org>
Reviewed-by: Mark Rutland <mark.rutland@arm.com>
Cc: Mark Rutland <mark.rutland@arm.com>
Cc: Catalin Marinas <catalin.marinas@arm.com>
Cc: Andrey Ryabinin <ryabinin.a.a@gmail.com>
Cc: Lorenzo Pieralisi <lorenzo.pieralisi@arm.com>
Cc: Alexander Potapenko <glider@google.com>
Cc: Will Deacon <will.deacon@arm.com>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Ananth N Mavinakayanahalli <ananth@linux.vnet.ibm.com>
Cc: Anil S Keshavamurthy <anil.s.keshavamurthy@intel.com>
Cc: "David S. Miller" <davem@davemloft.net>
Cc: Masami Hiramatsu <mhiramat@kernel.org>
Cc: kasan-dev@googlegroups.com
Cc: surovegin@google.com
Cc: rostedt@goodmis.org
Link: http://lkml.kernel.org/r/1476454043-101898-1-git-send-email-dvyukov@google.com


Signed-off-by: Ingo Molnar <mingo@kernel.org>

parent 9254139a

arch/arm64/kernel/sleep.S

+1 −1

Original line number	Diff line number	Diff line
		@@ -135,7 +135,7 @@ ENTRY(_cpu_resume)

		#ifdef CONFIG_KASAN
		mov x0, sp
		bl kasan_unpoison_remaining_stack
		bl kasan_unpoison_task_stack_below
		#endif

		ldp x19, x20, [x29, #16]

arch/x86/kernel/kprobes/core.c

+4 −0

Original line number	Diff line number	Diff line
		@@ -50,6 +50,7 @@
		#include <linux/kallsyms.h>
		#include <linux/ftrace.h>
		#include <linux/frame.h>
		#include <linux/kasan.h>

		#include <asm/text-patching.h>
		#include <asm/cacheflush.h>
		@@ -1081,6 +1082,9 @@ void jprobe_return(void)
		{
		struct kprobe_ctlblk *kcb = get_kprobe_ctlblk();

		/* Unpoison stack redzones in the frames we are going to jump over. */
		kasan_unpoison_stack_above_sp_to(kcb->jprobe_saved_sp);

		asm volatile (
		#ifdef CONFIG_X86_64
		" xchg %%rbx,%%rsp \n"

include/linux/kasan.h

+2 −0

Original line number	Diff line number	Diff line
		@@ -44,6 +44,7 @@ static inline void kasan_disable_current(void)
		void kasan_unpoison_shadow(const void *address, size_t size);

		void kasan_unpoison_task_stack(struct task_struct *task);
		void kasan_unpoison_stack_above_sp_to(const void *watermark);

		void kasan_alloc_pages(struct page *page, unsigned int order);
		void kasan_free_pages(struct page *page, unsigned int order);
		@@ -85,6 +86,7 @@ size_t kasan_metadata_size(struct kmem_cache *cache);
		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_unpoison_stack_above_sp_to(const void *watermark) {}

		static inline void kasan_enable_current(void) {}
		static inline void kasan_disable_current(void) {}

mm/kasan/kasan.c

+19 −3

Original line number	Diff line number	Diff line
		@@ -34,6 +34,7 @@
		#include <linux/string.h>
		#include <linux/types.h>
		#include <linux/vmalloc.h>
		#include <linux/bug.h>

		#include "kasan.h"
		#include "../slab.h"
		@@ -62,7 +63,7 @@ void kasan_unpoison_shadow(const void *address, size_t size)
		}
		}

		static void __kasan_unpoison_stack(struct task_struct task, void sp)
		static void __kasan_unpoison_stack(struct task_struct task, const void sp)
		{
		void *base = task_stack_page(task);
		size_t size = sp - base;
		@@ -77,9 +78,24 @@ void kasan_unpoison_task_stack(struct task_struct *task)
		}

		/* Unpoison the stack for the current task beyond a watermark sp value. */
		asmlinkage void kasan_unpoison_remaining_stack(void *sp)
		asmlinkage void kasan_unpoison_task_stack_below(const void *watermark)
		{
		__kasan_unpoison_stack(current, sp);
		__kasan_unpoison_stack(current, watermark);
		}

		/*
		* Clear all poison for the region between the current SP and a provided
		* watermark value, as is sometimes required prior to hand-crafted asm function
		* returns in the middle of functions.
		*/
		void kasan_unpoison_stack_above_sp_to(const void *watermark)
		{
		const void *sp = __builtin_frame_address(0);
		size_t size = watermark - sp;

		if (WARN_ON(sp > watermark))
		return;
		kasan_unpoison_shadow(sp, size);
		}

		/*

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