linux-kernel - [PATCH v1 bitops] bitops: Fix UBSAN undefined behavior warning for rotation right

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Date:   Sun,  7 Apr 2019 12:53:25 +0000
From:   Vadim Pasternak <vadimp@...lanox.com>
To:     jacek.anaszewski@...il.com, pavel@....cz, akpm@...ux-foundation.org
Cc:     linux-kernel@...r.kernel.org, linux-leds@...r.kernel.org,
        idosch@...lanox.com, Vadim Pasternak <vadimp@...lanox.com>
Subject: [PATCH v1 bitops] bitops: Fix UBSAN undefined behavior warning for rotation right

The warning is caused by call to rorXX(), if the second parameters of
this function "shift" is zero. In such case UBSAN reports the warning
for the next expression: (word << (XX - shift), where XX is
64, 32, 16, 8 for respectively ror64, ror32, ror16, ror8.
Fix adds validation of this parameter - in case it's equal zero, no
need to rotate, just original "word" is to be returned to caller.

The UBSAN undefined behavior warning has been reported for call to
ror32():
[   11.426543] UBSAN: Undefined behaviour in ./include/linux/bitops.h:93:33
[   11.434045] shift exponent 32 is too large for 32-bit type 'unsigned int'
[   11.441647] Hardware name: Mellanox Technologies Ltd. MSN3800/VMOD0007, BIOS 5.11 01/06/2019
[   11.441650] Call Trace:
[   11.441661]  dump_stack+0x71/0xab
[   11.441668]  ubsan_epilogue+0x9/0x49
[   11.441676]  __ubsan_handle_shift_out_of_bounds+0x1ea/0x241
[   11.441683]  ? __ubsan_handle_load_invalid_value+0x137/0x137
[   11.441691]  ? __module_text_address+0x11/0x90
[   11.441697]  ? widen_string+0x27/0x140
[   11.441704]  ? regmap_readable+0x76/0xc0
[   11.441709]  ? regmap_readable+0x76/0xc0
[   11.441718]  ? mlxplat_mlxcpld_readable_reg+0x1f/0x30 [mlx_platform]
[   11.441723]  ? regmap_volatile+0x40/0xb0
[   11.441729]  ? mlxplat_mlxcpld_volatile_reg+0x1f/0x30 [mlx_platform]
[   11.441735]  ? _regmap_read+0x11c/0x210
[   11.441741]  ? __mutex_lock_slowpath+0x10/0x10
[   11.441750]  ? mlxreg_led_store_hw+0x191/0x270 [leds_mlxreg]
[   11.441756]  mlxreg_led_store_hw+0x191/0x270 [leds_mlxreg]
[   11.441764]  ? mlxreg_led_brightness_get+0x270/0x270 [leds_mlxreg]
[   11.441769]  ? del_timer+0xe0/0xe0
[   11.441776]  ? bust_spinlocks+0x90/0x90
[   11.441784]  led_blink_setup+0x47/0x1d0
[   11.441792]  timer_trig_activate+0x8f/0x175 [ledtrig_timer]
[   11.441799]  ? kvasprintf_const+0xb0/0xb0
[   11.441805]  ? led_delay_on_show+0x50/0x50 [ledtrig_timer]
[   11.441810]  ? _raw_write_lock_bh+0xe0/0xe0
[   11.441815]  ? _raw_read_lock_irqsave+0x80/0x80
[   11.441822]  led_trigger_set+0x2cf/0x4d0
[   11.441829]  ? led_trigger_show+0x1f0/0x1f0
[   11.441834]  ? __mutex_lock_slowpath+0x10/0x10
[   11.441840]  ? kernfs_get_active+0xb2/0x120
[   11.441845]  ? kernfs_get_parent+0x50/0x50
[   11.441851]  led_trigger_store+0xe7/0x130
[   11.441858]  kernfs_fop_write+0x19a/0x250
[   11.441863]  ? sysfs_kf_bin_read+0x120/0x120
[   11.441869]  vfs_write+0xf5/0x230
[   11.441875]  ksys_write+0xa1/0x120
[   11.441881]  ? __ia32_sys_read+0x50/0x50
[   11.441888]  ? __do_page_fault+0x3e4/0x640
[   11.441895]  do_syscall_64+0x73/0x160
[   11.441900]  entry_SYSCALL_64_after_hwframe+0x44/0xa9
[   11.441905] RIP: 0033:0x7f955749f730
[   11.441911] Code: 73 01 c3 48 8b 0d 68 d7 2b 00 f7 d8 64 89 01 48 83 c8 ff c3 66 0f 1f 44 00 00 83 3d d9 2f 2c 00 00 75 10 b8 01 00 00 00 0f 05 <48> 3d 01 f0 ff ff 73 31 c3 48 83 ec 08 e8 7e 9b 01 00 48 89 04 24
[   11.441914] RSP: 002b:00007ffd4da04488 EFLAGS: 00000246 ORIG_RAX: 0000000000000001
[   11.441920] RAX: ffffffffffffffda RBX: 0000000000000006 RCX: 00007f955749f730
[   11.441923] RDX: 0000000000000006 RSI: 0000000001a14408 RDI: 0000000000000001
[   11.441926] RBP: 0000000001a14408 R08: 00007f955775f760 R09: 00007f9557da9b40
[   11.441929] R10: 0000000000000097 R11: 0000000000000246 R12: 0000000000000006
[   11.441932] R13: 0000000000000001 R14: 00007f955775e600 R15: 0000000000000006

Reported-by: Ido Schimmel <idosch@...lanox.com>
Signed-off-by: Vadim Pasternak <vadimp@...lanox.com>
---
 include/linux/bitops.h | 12 ++++++++++++
 1 file changed, 12 insertions(+)

diff --git a/include/linux/bitops.h b/include/linux/bitops.h
index 602af23b98c7..02c00f3c8205 100644
--- a/include/linux/bitops.h
+++ b/include/linux/bitops.h
@@ -70,6 +70,9 @@ static inline __u64 rol64(__u64 word, unsigned int shift)
  */
 static inline __u64 ror64(__u64 word, unsigned int shift)
 {
+	if (!shift)
+		return word;
+
 	return (word >> shift) | (word << (64 - shift));
 }
 
@@ -90,6 +93,9 @@ static inline __u32 rol32(__u32 word, unsigned int shift)
  */
 static inline __u32 ror32(__u32 word, unsigned int shift)
 {
+	if (!shift)
+		return word;
+
 	return (word >> shift) | (word << (32 - shift));
 }
 
@@ -110,6 +116,9 @@ static inline __u16 rol16(__u16 word, unsigned int shift)
  */
 static inline __u16 ror16(__u16 word, unsigned int shift)
 {
+	if (!shift)
+		return word;
+
 	return (word >> shift) | (word << (16 - shift));
 }
 
@@ -130,6 +139,9 @@ static inline __u8 rol8(__u8 word, unsigned int shift)
  */
 static inline __u8 ror8(__u8 word, unsigned int shift)
 {
+	if (!shift)
+		return word;
+
 	return (word >> shift) | (word << (8 - shift));
 }
 
-- 
2.11.0