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 <dvyu...@google.com>
Cc: Mark Rutland <mark.rutl...@arm.com>
Cc: Catalin Marinas <catalin.mari...@arm.com>
Cc: Andrey Ryabinin <ryabinin....@gmail.com>
Cc: Lorenzo Pieralisi <lorenzo.pieral...@arm.com>
Cc: Alexander Potapenko <gli...@google.com>
Cc: Will Deacon <will.dea...@arm.com>
Cc: Ingo Molnar <mi...@kernel.org>
Cc: Andrew Morton <a...@linux-foundation.org>
Cc: Thomas Gleixner <t...@linutronix.de>
Cc: "H. Peter Anvin" <h...@zytor.com>
Cc: Ananth N Mavinakayanahalli <ana...@linux.vnet.ibm.com>
Cc: Anil S Keshavamurthy <anil.s.keshavamur...@intel.com>
Cc: "David S. Miller" <da...@davemloft.net>
Cc: Masami Hiramatsu <mhira...@kernel.org>
Cc: x...@kernel.org
Cc: kasan-...@googlegroups.com

--

Changes since v1:
 - leave kasan_unpoison_remaining_stack() intact
 - instead add kasan_unpoison_stack_above_sp_to()
 - rename kasan_unpoison_remaining_stack() to kasan_unpoison_task_stack_below()

Changes since v2:
 - fix build by adding return type to kasan_unpoison_stack_above_sp_to
   (tested v2 with it, but forgot to git add)

I observe false positives due to this in sctp code.
sctp uses jprobe_return() in jsctp_sf_eat_sack().
The stray 0xf4 in shadow memory are stack redzones.

[  376.492209] 
==================================================================
[  376.500368] BUG: KASAN: stack-out-of-bounds in memcmp+0xe9/0x150 at addr 
ffff88005e48f480
[  376.509522] Read of size 1 by task syz-executor/18535
[  376.515249] page:ffffea00017923c0 count:0 mapcount:0 mapping:          
(null) index:0x0
[  376.524377] flags: 0x1fffc0000000000()
[  376.528645] page dumped because: kasan: bad access detected
[  376.534939] CPU: 1 PID: 18535 Comm: syz-executor Not tainted 4.8.0+ #28
[  376.542375] Hardware name: Google Google Compute Engine/Google Compute 
Engine, BIOS Google 01/01/2011
[  376.552669]  ffff88005e48f2d0 ffffffff82d2b849 ffffffff0bc91e90 
fffffbfff10971e8
[  376.561599]  ffffed000bc91e90 ffffed000bc91e90 0000000000000001 
0000000000000000
[  376.570486]  ffff88005e48f480 ffff88005e48f350 ffffffff817d3169 
ffff88005e48f370
[  376.579348] Call Trace:
[  376.582196]  [<ffffffff82d2b849>] dump_stack+0x12e/0x185
[  376.588190]  [<ffffffff817d3169>] kasan_report+0x489/0x4b0
[  376.594378]  [<ffffffff82d49529>] ? memcmp+0xe9/0x150
[  376.600099]  [<ffffffff8126377e>] ? update_stack_state.constprop.4+0xde/0x150
[  376.608187]  [<ffffffff817d31a9>] __asan_report_load1_noabort+0x19/0x20
[  376.615620]  [<ffffffff82d49529>] memcmp+0xe9/0x150
[  376.621148]  [<ffffffff82df7486>] depot_save_stack+0x176/0x5c0
[  376.627722]  [<ffffffff85b03f19>] ? skb_free_head+0x79/0xb0
[  376.634006]  [<ffffffff817d2031>] save_stack+0xb1/0xd0
[  376.639805]  [<ffffffff811fc8ab>] ? save_stack_trace+0x1b/0x20
[  376.646369]  [<ffffffff817d1fc6>] ? save_stack+0x46/0xd0
[  376.652366]  [<ffffffff817d27f2>] ? kasan_slab_free+0x72/0xc0
[  376.658837]  [<ffffffff817d05b8>] ? kfree+0xc8/0x2a0
[  376.664454]  [<ffffffff85b03f19>] ? skb_free_head+0x79/0xb0
[  376.670736]  [<ffffffff85b0900a>] ? skb_release_data+0x37a/0x420
[  376.677517]  [<ffffffff85b090ff>] ? skb_release_all+0x4f/0x60
[  376.683992]  [<ffffffff85b11348>] ? consume_skb+0x138/0x370
[  376.690284]  [<ffffffff8676ad7b>] ? sctp_chunk_put+0xcb/0x180
[  376.696761]  [<ffffffff8676ae88>] ? sctp_chunk_free+0x58/0x70
[  376.703234]  [<ffffffff8677fa5f>] ? sctp_inq_pop+0x68f/0xef0
[  376.709616]  [<ffffffff8675ee36>] ? sctp_assoc_bh_rcv+0xd6/0x4b0
[  376.716379]  [<ffffffff8677f2c1>] ? sctp_inq_push+0x131/0x190
[  376.722946]  [<ffffffff867bad69>] ? sctp_backlog_rcv+0xe9/0xa20
[  376.729615]  [<ffffffff85af70dc>] ? __release_sock+0x12c/0x3a0
[  376.736186]  [<ffffffff85af73ae>] ? release_sock+0x5e/0x1c0
[  376.742465]  [<ffffffff8679fc62>] ? sctp_sendmsg+0xd82/0x2e00
[  376.748935]  [<ffffffff85f83c43>] ? inet_sendmsg+0x303/0x4c0
[  376.755318]  [<ffffffff85aeab0f>] ? sock_sendmsg+0xcf/0x110
[  376.761599]  [<ffffffff85aebc1d>] ? SYSC_sendto+0x20d/0x340
[  376.767882]  [<ffffffff85aee175>] ? SyS_sendto+0x45/0x60
[  376.773885]  [<ffffffff81008783>] ? do_syscall_64+0x1d3/0x620
[  376.780372]  [<ffffffff86d8e9cd>] ? entry_SYSCALL64_slow_path+0x25/0x25
[  376.787832]  [<ffffffff86751c79>] ? sctp_do_sm+0x3689/0x4e90
[  376.794215]  [<ffffffff81467040>] ? debug_check_no_locks_freed+0x3c0/0x3c0
[  376.801948]  [<ffffffff8674e5f0>] ? 
sctp_do_8_2_transport_strike.isra.19+0x900/0x900
[  376.810918]  [<ffffffff81466ed0>] ? debug_check_no_locks_freed+0x250/0x3c0
[  376.818650]  [<ffffffff817d27f2>] kasan_slab_free+0x72/0xc0
[  376.824945]  [<ffffffff817d05b8>] kfree+0xc8/0x2a0
[  376.830374]  [<ffffffff85b03f19>] skb_free_head+0x79/0xb0
[  376.836466]  [<ffffffff85b0900a>] skb_release_data+0x37a/0x420
[  376.843036]  [<ffffffff85b090ff>] skb_release_all+0x4f/0x60
[  376.849319]  [<ffffffff85b11348>] consume_skb+0x138/0x370
[  376.855411]  [<ffffffff8676ad7b>] sctp_chunk_put+0xcb/0x180
[  376.861702]  [<ffffffff8676ae88>] sctp_chunk_free+0x58/0x70
[  376.867990]  [<ffffffff8677fa5f>] sctp_inq_pop+0x68f/0xef0
[  376.874182]  [<ffffffff8675ee36>] sctp_assoc_bh_rcv+0xd6/0x4b0
[  376.880759]  [<ffffffff8677f2c1>] sctp_inq_push+0x131/0x190
[  376.887055]  [<ffffffff867bad69>] sctp_backlog_rcv+0xe9/0xa20
[  376.893532]  [<ffffffff814667dd>] ? trace_hardirqs_on+0xd/0x10
[  376.900107]  [<ffffffff81369bed>] ? __local_bh_enable_ip+0xad/0x190
[  376.907161]  [<ffffffff85af70dc>] __release_sock+0x12c/0x3a0
[  376.913540]  [<ffffffff85af73ae>] release_sock+0x5e/0x1c0
[  376.919922]  [<ffffffff8679fc62>] sctp_sendmsg+0xd82/0x2e00
[  376.926209]  [<ffffffff8679eee0>] ? sctp_id2assoc+0x330/0x330
[  376.932696]  [<ffffffff81467040>] ? debug_check_no_locks_freed+0x3c0/0x3c0
[  376.940417]  [<ffffffff814a6127>] ? debug_lockdep_rcu_enabled+0x77/0x90
[  376.947858]  [<ffffffff814a6127>] ? debug_lockdep_rcu_enabled+0x77/0x90
[  376.955293]  [<ffffffff85f83940>] ? inet_recvmsg+0x4b0/0x4b0
[  376.961675]  [<ffffffff85f83b48>] ? inet_sendmsg+0x208/0x4c0
[  376.968064]  [<ffffffff85f83c43>] inet_sendmsg+0x303/0x4c0
[  376.974261]  [<ffffffff85f839b8>] ? inet_sendmsg+0x78/0x4c0
[  376.980546]  [<ffffffff85f83940>] ? inet_recvmsg+0x4b0/0x4b0
[  376.986929]  [<ffffffff85aeab0f>] sock_sendmsg+0xcf/0x110
[  376.993025]  [<ffffffff85aebc1d>] SYSC_sendto+0x20d/0x340
[  376.999125]  [<ffffffff85aeba10>] ? SYSC_connect+0x2e0/0x2e0
[  377.005510]  [<ffffffff8188cc33>] ? __fd_install+0x233/0x560
[  377.011894]  [<ffffffff81007b93>] ? perf_trace_sys_enter+0x443/0x9d0
[  377.019051]  [<ffffffff81007750>] ? syscall_trace_enter+0xe00/0xe00
[  377.026109]  [<ffffffff8158887f>] ? __sanitizer_cov_trace_pc+0x4f/0x60
[  377.033466]  [<ffffffff85aee175>] SyS_sendto+0x45/0x60
[  377.039278]  [<ffffffff85aee130>] ? SyS_getpeername+0x30/0x30
[  377.045752]  [<ffffffff81008783>] do_syscall_64+0x1d3/0x620
[  377.052035]  [<ffffffff8100501a>] ? trace_hardirqs_on_thunk+0x1a/0x1c
[  377.059281]  [<ffffffff86d8e9cd>] entry_SYSCALL64_slow_path+0x25/0x25
[  377.066509] Memory state around the buggy address:
[  377.071935]  ffff88005e48f380: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 
00
[  377.080024]  ffff88005e48f400: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 
00
[  377.088117] >ffff88005e48f480: f4 f4 00 00 00 00 00 00 00 00 00 00 00 00 00 
00
[  377.096205]                    ^
[  377.099900]  ffff88005e48f500: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 
00
[  377.107994]  ffff88005e48f580: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 
00
[  377.116079] 
==================================================================
---
 arch/arm64/kernel/sleep.S      |  2 +-
 arch/x86/kernel/kprobes/core.c |  4 ++++
 include/linux/kasan.h          |  2 ++
 mm/kasan/kasan.c               | 19 +++++++++++++++++--
 4 files changed, 24 insertions(+), 3 deletions(-)

diff --git a/arch/arm64/kernel/sleep.S b/arch/arm64/kernel/sleep.S
index b8799e7..1bec41b 100644
--- a/arch/arm64/kernel/sleep.S
+++ b/arch/arm64/kernel/sleep.S
@@ -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]
diff --git a/arch/x86/kernel/kprobes/core.c b/arch/x86/kernel/kprobes/core.c
index 28cee01..22a462a 100644
--- a/arch/x86/kernel/kprobes/core.c
+++ b/arch/x86/kernel/kprobes/core.c
@@ -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>
@@ -1080,6 +1081,9 @@ 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"
diff --git a/include/linux/kasan.h b/include/linux/kasan.h
index d600303..820c0ad 100644
--- a/include/linux/kasan.h
+++ b/include/linux/kasan.h
@@ -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) {}
diff --git a/mm/kasan/kasan.c b/mm/kasan/kasan.c
index 88af13c..52d7ff1 100644
--- a/mm/kasan/kasan.c
+++ b/mm/kasan/kasan.c
@@ -77,9 +77,24 @@ 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 = (void *)current_stack_pointer();
+       size_t size = watermark - sp;
+
+       if (WARN_ON(sp > watermark))
+               return;
+       kasan_unpoison_shadow(sp, size);
 }
 
 /*
-- 
2.8.0.rc3.226.g39d4020

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