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From:   Andrew Jeffery <andrew@aj.id.au>
To:     linux-arm-kernel@lists.infradead.org
Cc:     linux@armlinux.org.uk, mhiramat@kernel.org, labbott@redhat.com,
        keescook@chromium.org, mathieu.desnoyers@efficios.com,
        linux-kernel@vger.kernel.org,
        Luka Oreskovic <luka.oreskovic@sartura.hr>,
        Juraj Vijtiuk <juraj.vijtiuk@sartura.hr>
Subject: [PATCH v2] ARM: kprobes: Avoid fortify_panic() when copying optprobe template
Date:   Thu,  1 Oct 2020 13:59:27 +0930
Message-Id: <20201001042927.2147800-1-andrew@aj.id.au>
MIME-Version: 1.0
Content-Transfer-Encoding: 8bit
Precedence: bulk

Setting both CONFIG_KPROBES=y and CONFIG_FORTIFY_SOURCE=y on ARM leads
to a panic in memcpy() when injecting a kprobe despite the fixes found
in commit e46daee53bb5 ("ARM: 8806/1: kprobes: Fix false positive with
FORTIFY_SOURCE") and commit 0ac569bf6a79 ("ARM: 8834/1: Fix: kprobes:
optimized kprobes illegal instruction").

arch/arm/include/asm/kprobes.h effectively declares
the target type of the optprobe_template_entry assembly label as a u32
which leads memcpy()'s __builtin_object_size() call to determine that
the pointed-to object is of size four. However, the symbol is used as a handle
for the optimised probe assembly template that is at least 96 bytes in size.
The symbol's use despite its type blows up the memcpy() in ARM's
arch_prepare_optimized_kprobe() with a false-positive fortify_panic() when it
should instead copy the optimised probe template into place:

```
$ sudo perf probe -a aspeed_g6_pinctrl_probe
[  158.457252] detected buffer overflow in memcpy
[  158.458069] ------------[ cut here ]------------
[  158.458283] kernel BUG at lib/string.c:1153!
[  158.458436] Internal error: Oops - BUG: 0 [#1] SMP ARM
[  158.458768] Modules linked in:
[  158.459043] CPU: 1 PID: 99 Comm: perf Not tainted 5.9.0-rc7-00038-gc53ebf8167e9 #158
[  158.459296] Hardware name: Generic DT based system
[  158.459529] PC is at fortify_panic+0x18/0x20
[  158.459658] LR is at __irq_work_queue_local+0x3c/0x74
[  158.459831] pc : [<8047451c>]    lr : [<8020ecd4>]    psr: 60000013
[  158.460032] sp : be2d1d50  ip : be2d1c58  fp : be2d1d5c
[  158.460174] r10: 00000006  r9 : 00000000  r8 : 00000060
[  158.460348] r7 : 8011e434  r6 : b9e0b800  r5 : 7f000000  r4 : b9fe4f0c
[  158.460557] r3 : 80c04cc8  r2 : 00000000  r1 : be7c03cc  r0 : 00000022
[  158.460801] Flags: nZCv  IRQs on  FIQs on  Mode SVC_32  ISA ARM  Segment none
[  158.461037] Control: 10c5387d  Table: b9cd806a  DAC: 00000051
[  158.461251] Process perf (pid: 99, stack limit = 0x81c71a69)
[  158.461472] Stack: (0xbe2d1d50 to 0xbe2d2000)
[  158.461757] 1d40:                                     be2d1d84 be2d1d60 8011e724 80474510
[  158.462104] 1d60: b9e0b800 b9fe4f0c 00000000 b9fe4f14 80c8ec80 be235000 be2d1d9c be2d1d88
[  158.462436] 1d80: 801cee44 8011e57c b9fe4f0c 00000000 be2d1dc4 be2d1da0 801d0ad0 801cedec
[  158.462742] 1da0: 00000000 00000000 b9fe4f00 ffffffea 00000000 be235000 be2d1de4 be2d1dc8
[  158.463087] 1dc0: 80204604 801d0738 00000000 00000000 b9fe4004 ffffffea be2d1e94 be2d1de8
[  158.463428] 1de0: 80205434 80204570 00385c00 00000000 00000000 00000000 be2d1e14 be2d1e08
[  158.463880] 1e00: 802ba014 b9fe4f00 b9e718c0 b9fe4f84 b9e71ec8 be2d1e24 00000000 00385c00
[  158.464365] 1e20: 00000000 626f7270 00000065 802b905c be2d1e94 0000002e 00000000 802b9914
[  158.464829] 1e40: be2d1e84 be2d1e50 802b9914 8028ff78 804629d0 b9e71ec0 0000002e b9e71ec0
[  158.465141] 1e60: be2d1ea8 80c04cc8 00000cc0 b9e713c4 00000002 80205834 80205834 0000002e
[  158.465488] 1e80: be235000 be235000 be2d1ea4 be2d1e98 80205854 80204e94 be2d1ecc be2d1ea8
[  158.465806] 1ea0: 801ee4a0 80205840 00000002 80c04cc8 00000000 0000002e 0000002e 00000000
[  158.466110] 1ec0: be2d1f0c be2d1ed0 801ee5c8 801ee428 00000000 be2d0000 006b1fd0 00000051
[  158.466398] 1ee0: 00000000 b9eedf00 0000002e 80204410 006b1fd0 be2d1f60 00000000 00000004
[  158.466763] 1f00: be2d1f24 be2d1f10 8020442c 801ee4c4 80205834 802c613c be2d1f5c be2d1f28
[  158.467102] 1f20: 802c60ac 8020441c be2d1fac be2d1f38 8010c764 802e9888 be2d1f5c b9eedf00
[  158.467447] 1f40: b9eedf00 006b1fd0 0000002e 00000000 be2d1f94 be2d1f60 802c634c 802c5fec
[  158.467812] 1f60: 00000000 00000000 00000000 80c04cc8 006b1fd0 00000003 76f7a610 00000004
[  158.468155] 1f80: 80100284 be2d0000 be2d1fa4 be2d1f98 802c63ec 802c62e8 00000000 be2d1fa8
[  158.468508] 1fa0: 80100080 802c63e0 006b1fd0 00000003 00000003 006b1fd0 0000002e 00000000
[  158.468858] 1fc0: 006b1fd0 00000003 76f7a610 00000004 006b1fb0 0026d348 00000017 7ef2738c
[  158.469202] 1fe0: 76f3431c 7ef272d8 0014ec50 76f34338 60000010 00000003 00000000 00000000
[  158.469461] Backtrace:
[  158.469683] [<80474504>] (fortify_panic) from [<8011e724>] (arch_prepare_optimized_kprobe+0x1b4/0x1f8)
[  158.470021] [<8011e570>] (arch_prepare_optimized_kprobe) from [<801cee44>] (alloc_aggr_kprobe+0x64/0x70)
[  158.470287]  r9:be235000 r8:80c8ec80 r7:b9fe4f14 r6:00000000 r5:b9fe4f0c r4:b9e0b800
[  158.470478] [<801cede0>] (alloc_aggr_kprobe) from [<801d0ad0>] (register_kprobe+0x3a4/0x5a0)
[  158.470685]  r5:00000000 r4:b9fe4f0c
[  158.470790] [<801d072c>] (register_kprobe) from [<80204604>] (__register_trace_kprobe+0xa0/0xa4)
[  158.471001]  r9:be235000 r8:00000000 r7:ffffffea r6:b9fe4f00 r5:00000000 r4:00000000
[  158.471188] [<80204564>] (__register_trace_kprobe) from [<80205434>] (trace_kprobe_create+0x5ac/0x9ac)
[  158.471408]  r7:ffffffea r6:b9fe4004 r5:00000000 r4:00000000
[  158.471553] [<80204e88>] (trace_kprobe_create) from [<80205854>] (create_or_delete_trace_kprobe+0x20/0x3c)
[  158.471766]  r10:be235000 r9:be235000 r8:0000002e r7:80205834 r6:80205834 r5:00000002
[  158.471949]  r4:b9e713c4
[  158.472027] [<80205834>] (create_or_delete_trace_kprobe) from [<801ee4a0>] (trace_run_command+0x84/0x9c)
[  158.472255] [<801ee41c>] (trace_run_command) from [<801ee5c8>] (trace_parse_run_command+0x110/0x1f8)
[  158.472471]  r6:00000000 r5:0000002e r4:0000002e
[  158.472594] [<801ee4b8>] (trace_parse_run_command) from [<8020442c>] (probes_write+0x1c/0x28)
[  158.472800]  r10:00000004 r9:00000000 r8:be2d1f60 r7:006b1fd0 r6:80204410 r5:0000002e
[  158.472968]  r4:b9eedf00
[  158.473046] [<80204410>] (probes_write) from [<802c60ac>] (vfs_write+0xcc/0x1e8)
[  158.473226] [<802c5fe0>] (vfs_write) from [<802c634c>] (ksys_write+0x70/0xf8)
[  158.473400]  r8:00000000 r7:0000002e r6:006b1fd0 r5:b9eedf00 r4:b9eedf00
[  158.473567] [<802c62dc>] (ksys_write) from [<802c63ec>] (sys_write+0x18/0x1c)
[  158.473745]  r9:be2d0000 r8:80100284 r7:00000004 r6:76f7a610 r5:00000003 r4:006b1fd0
[  158.473932] [<802c63d4>] (sys_write) from [<80100080>] (ret_fast_syscall+0x0/0x54)
[  158.474126] Exception stack(0xbe2d1fa8 to 0xbe2d1ff0)
[  158.474305] 1fa0:                   006b1fd0 00000003 00000003 006b1fd0 0000002e 00000000
[  158.474573] 1fc0: 006b1fd0 00000003 76f7a610 00000004 006b1fb0 0026d348 00000017 7ef2738c
[  158.474811] 1fe0: 76f3431c 7ef272d8 0014ec50 76f34338
[  158.475171] Code: e24cb004 e1a01000 e59f0004 ebf40dd3 (e7f001f2)
[  158.475847] ---[ end trace 55a5b31c08a29f00 ]---
[  158.476088] Kernel panic - not syncing: Fatal exception
[  158.476375] CPU0: stopping
[  158.476709] CPU: 0 PID: 0 Comm: swapper/0 Tainted: G      D           5.9.0-rc7-00038-gc53ebf8167e9 #158
[  158.477176] Hardware name: Generic DT based system
[  158.477411] Backtrace:
[  158.477604] [<8010dd28>] (dump_backtrace) from [<8010dfd4>] (show_stack+0x20/0x24)
[  158.477990]  r7:00000000 r6:60000193 r5:00000000 r4:80c2f634
[  158.478323] [<8010dfb4>] (show_stack) from [<8046390c>] (dump_stack+0xcc/0xe8)
[  158.478686] [<80463840>] (dump_stack) from [<80110750>] (handle_IPI+0x334/0x3a0)
[  158.479063]  r7:00000000 r6:00000004 r5:80b65cc8 r4:80c78278
[  158.479352] [<8011041c>] (handle_IPI) from [<801013f8>] (gic_handle_irq+0x88/0x94)
[  158.479757]  r10:10c5387d r9:80c01ed8 r8:00000000 r7:c0802000 r6:80c0537c r5:000003ff
[  158.480146]  r4:c080200c r3:fffffff4
[  158.480364] [<80101370>] (gic_handle_irq) from [<80100b6c>] (__irq_svc+0x6c/0x90)
[  158.480748] Exception stack(0x80c01ed8 to 0x80c01f20)
[  158.481031] 1ec0:                                                       000128bc 00000000
[  158.481499] 1ee0: be7b8174 8011d3a0 80c00000 00000000 80c04cec 80c04d28 80c5d7c2 80a026d4
[  158.482091] 1f00: 10c5387d 80c01f34 80c01f38 80c01f28 80109554 80109558 60000013 ffffffff
[  158.482621]  r9:80c00000 r8:80c5d7c2 r7:80c01f0c r6:ffffffff r5:60000013 r4:80109558
[  158.482983] [<80109518>] (arch_cpu_idle) from [<80818780>] (default_idle_call+0x38/0x120)
[  158.483360] [<80818748>] (default_idle_call) from [<801585a8>] (do_idle+0xd4/0x158)
[  158.483945]  r5:00000000 r4:80c00000
[  158.484237] [<801584d4>] (do_idle) from [<801588f4>] (cpu_startup_entry+0x28/0x2c)
[  158.484784]  r9:80c78000 r8:00000000 r7:80c78000 r6:80c78040 r5:80c04cc0 r4:000000d6
[  158.485328] [<801588cc>] (cpu_startup_entry) from [<80810a78>] (rest_init+0x9c/0xbc)
[  158.485930] [<808109dc>] (rest_init) from [<80b00ae4>] (arch_call_rest_init+0x18/0x1c)
[  158.486503]  r5:80c04cc0 r4:00000001
[  158.486857] [<80b00acc>] (arch_call_rest_init) from [<80b00fcc>] (start_kernel+0x46c/0x548)
[  158.487589] [<80b00b60>] (start_kernel) from [<00000000>] (0x0)
```

Fixes: e46daee53bb5 ("ARM: 8806/1: kprobes: Fix false positive with FORTIFY_SOURCE")
Fixes: 0ac569bf6a79 ("ARM: 8834/1: Fix: kprobes: optimized kprobes illegal instruction")
Cc: Luka Oreskovic <luka.oreskovic@sartura.hr>
Cc: Juraj Vijtiuk <juraj.vijtiuk@sartura.hr>
Suggested-by: Kees Cook <keescook@chromium.org>
Signed-off-by: Andrew Jeffery <andrew@aj.id.au>
---
v1 was sent some time back, in May:

https://lore.kernel.org/linux-arm-kernel/20200517153959.293224-1-andrew@aj.id.au/

I've taken the patch that Kees' suggested in the replies and tested it.
---
 arch/arm/include/asm/kprobes.h    | 22 +++++++++++-----------
 arch/arm/probes/kprobes/opt-arm.c | 18 +++++++++---------
 2 files changed, 20 insertions(+), 20 deletions(-)

diff --git a/arch/arm/include/asm/kprobes.h b/arch/arm/include/asm/kprobes.h
index 213607a1f45c..e26a278d301a 100644
--- a/arch/arm/include/asm/kprobes.h
+++ b/arch/arm/include/asm/kprobes.h
@@ -44,20 +44,20 @@ int kprobe_exceptions_notify(struct notifier_block *self,
 			     unsigned long val, void *data);
 
 /* optinsn template addresses */
-extern __visible kprobe_opcode_t optprobe_template_entry;
-extern __visible kprobe_opcode_t optprobe_template_val;
-extern __visible kprobe_opcode_t optprobe_template_call;
-extern __visible kprobe_opcode_t optprobe_template_end;
-extern __visible kprobe_opcode_t optprobe_template_sub_sp;
-extern __visible kprobe_opcode_t optprobe_template_add_sp;
-extern __visible kprobe_opcode_t optprobe_template_restore_begin;
-extern __visible kprobe_opcode_t optprobe_template_restore_orig_insn;
-extern __visible kprobe_opcode_t optprobe_template_restore_end;
+extern __visible kprobe_opcode_t optprobe_template_entry[];
+extern __visible kprobe_opcode_t optprobe_template_val[];
+extern __visible kprobe_opcode_t optprobe_template_call[];
+extern __visible kprobe_opcode_t optprobe_template_end[];
+extern __visible kprobe_opcode_t optprobe_template_sub_sp[];
+extern __visible kprobe_opcode_t optprobe_template_add_sp[];
+extern __visible kprobe_opcode_t optprobe_template_restore_begin[];
+extern __visible kprobe_opcode_t optprobe_template_restore_orig_insn[];
+extern __visible kprobe_opcode_t optprobe_template_restore_end[];
 
 #define MAX_OPTIMIZED_LENGTH	4
 #define MAX_OPTINSN_SIZE				\
-	((unsigned long)&optprobe_template_end -	\
-	 (unsigned long)&optprobe_template_entry)
+	((unsigned long)optprobe_template_end -	\
+	 (unsigned long)optprobe_template_entry)
 #define RELATIVEJUMP_SIZE	4
 
 struct arch_optimized_insn {
diff --git a/arch/arm/probes/kprobes/opt-arm.c b/arch/arm/probes/kprobes/opt-arm.c
index 7a449df0b359..c78180172120 100644
--- a/arch/arm/probes/kprobes/opt-arm.c
+++ b/arch/arm/probes/kprobes/opt-arm.c
@@ -85,21 +85,21 @@ asm (
 			"optprobe_template_end:\n");
 
 #define TMPL_VAL_IDX \
-	((unsigned long *)&optprobe_template_val - (unsigned long *)&optprobe_template_entry)
+	((unsigned long *)optprobe_template_val - (unsigned long *)optprobe_template_entry)
 #define TMPL_CALL_IDX \
-	((unsigned long *)&optprobe_template_call - (unsigned long *)&optprobe_template_entry)
+	((unsigned long *)optprobe_template_call - (unsigned long *)optprobe_template_entry)
 #define TMPL_END_IDX \
-	((unsigned long *)&optprobe_template_end - (unsigned long *)&optprobe_template_entry)
+	((unsigned long *)optprobe_template_end - (unsigned long *)optprobe_template_entry)
 #define TMPL_ADD_SP \
-	((unsigned long *)&optprobe_template_add_sp - (unsigned long *)&optprobe_template_entry)
+	((unsigned long *)optprobe_template_add_sp - (unsigned long *)optprobe_template_entry)
 #define TMPL_SUB_SP \
-	((unsigned long *)&optprobe_template_sub_sp - (unsigned long *)&optprobe_template_entry)
+	((unsigned long *)optprobe_template_sub_sp - (unsigned long *)optprobe_template_entry)
 #define TMPL_RESTORE_BEGIN \
-	((unsigned long *)&optprobe_template_restore_begin - (unsigned long *)&optprobe_template_entry)
+	((unsigned long *)optprobe_template_restore_begin - (unsigned long *)optprobe_template_entry)
 #define TMPL_RESTORE_ORIGN_INSN \
-	((unsigned long *)&optprobe_template_restore_orig_insn - (unsigned long *)&optprobe_template_entry)
+	((unsigned long *)optprobe_template_restore_orig_insn - (unsigned long *)optprobe_template_entry)
 #define TMPL_RESTORE_END \
-	((unsigned long *)&optprobe_template_restore_end - (unsigned long *)&optprobe_template_entry)
+	((unsigned long *)optprobe_template_restore_end - (unsigned long *)optprobe_template_entry)
 
 /*
  * ARM can always optimize an instruction when using ARM ISA, except
@@ -234,7 +234,7 @@ int arch_prepare_optimized_kprobe(struct optimized_kprobe *op, struct kprobe *or
 	}
 
 	/* Copy arch-dep-instance from template. */
-	memcpy(code, (unsigned long *)&optprobe_template_entry,
+	memcpy(code, (unsigned long *)optprobe_template_entry,
 			TMPL_END_IDX * sizeof(kprobe_opcode_t));
 
 	/* Adjust buffer according to instruction. */
-- 
2.25.1