On 2023-09-06 19:03, Will Deacon wrote:
From: Joey Gouly joey.gouly@arm.com
commit 387d828adffcf1eb949f3141079c479793c59aac upstream.
Import the latest version of the Arm Optimized Routines strncmp function based on the upstream code of string/aarch64/strncmp.S at commit 189dfefe37d5 from: https://github.com/ARM-software/optimized-routines
This latest version includes MTE support.
Note that for simplicity Arm have chosen to contribute this code to Linux under GPLv2 rather than the original MIT OR Apache-2.0 WITH LLVM-exception license. Arm is the sole copyright holder for this code.
Signed-off-by: Joey Gouly joey.gouly@arm.com Cc: Robin Murphy robin.murphy@arm.com Cc: Mark Rutland mark.rutland@arm.com Cc: Catalin Marinas catalin.marinas@arm.com Cc: Will Deacon will@kernel.org Acked-by: Mark Rutland mark.rutland@arm.com Acked-by: Catalin Marinas catalin.marinas@arm.com Link: https://lore.kernel.org/r/20220301101435.19327-3-joey.gouly@arm.com (cherry picked from commit 387d828adffcf1eb949f3141079c479793c59aac) Cc: stable@vger.kernel.org # 5.15.y only Fixes: 020b199bc70d ("arm64: Import latest version of Cortex Strings' strncmp") Reported-by: John Hsu John.Hsu@mediatek.com Link: https://lore.kernel.org/all/e9f30f7d5b7d72a3521da31ab2002b49a26f542e.camel@m... Signed-off-by: Will Deacon will@kernel.org
This is a clean cherry-pick of the latest MTE-safe strncmp() implementation for arm64 which landed in v5.18 and somewhat accidentally fixed an out-of-bounds read introduced in v5.14. An alternative would be to disable the optimised code altogether, but given that this is self-contained and applies cleanly, I'd favour being consistent with more recent kernels.
Ack to that; it's also consistent with the upstream project where it seems this bug wasn't found before the code was replaced with the new version either, so a more specific fix never existed.
Cheers, Robin.
arch/arm64/lib/strncmp.S | 244 +++++++++++++++++++++++---------------- 1 file changed, 146 insertions(+), 98 deletions(-)
diff --git a/arch/arm64/lib/strncmp.S b/arch/arm64/lib/strncmp.S index e42bcfcd37e6..a4884b97e9a8 100644 --- a/arch/arm64/lib/strncmp.S +++ b/arch/arm64/lib/strncmp.S @@ -1,9 +1,9 @@ /* SPDX-License-Identifier: GPL-2.0-only */ /*
- Copyright (c) 2013-2021, Arm Limited.
- Copyright (c) 2013-2022, Arm Limited.
- Adapted from the original at:
#include <linux/linkage.h> @@ -11,14 +11,14 @@ /* Assumptions:
- ARMv8-a, AArch64
- ARMv8-a, AArch64.
*/
- MTE compatible.
#define L(label) .L ## label #define REP8_01 0x0101010101010101 #define REP8_7f 0x7f7f7f7f7f7f7f7f -#define REP8_80 0x8080808080808080 /* Parameters and result. */ #define src1 x0 @@ -39,10 +39,24 @@ #define tmp3 x10 #define zeroones x11 #define pos x12 -#define limit_wd x13 -#define mask x14 -#define endloop x15 +#define mask x13 +#define endloop x14 #define count mask +#define offset pos +#define neg_offset x15
+/* Define endian dependent shift operations.
- On big-endian early bytes are at MSB and on little-endian LSB.
- LS_FW means shifting towards early bytes.
- LS_BK means shifting towards later bytes.
- */
+#ifdef __AARCH64EB__ +#define LS_FW lsl +#define LS_BK lsr +#else +#define LS_FW lsr +#define LS_BK lsl +#endif SYM_FUNC_START_WEAK_PI(strncmp) cbz limit, L(ret0) @@ -52,9 +66,6 @@ SYM_FUNC_START_WEAK_PI(strncmp) and count, src1, #7 b.ne L(misaligned8) cbnz count, L(mutual_align)
- /* Calculate the number of full and partial words -1. */
- sub limit_wd, limit, #1 /* limit != 0, so no underflow. */
- lsr limit_wd, limit_wd, #3 /* Convert to Dwords. */
/* NUL detection works on the principle that (X - 1) & (~X) & 0x80 (=> (X - 1) & ~(X | 0x7f)) is non-zero iff a byte is zero, and @@ -64,30 +75,45 @@ L(loop_aligned): ldr data1, [src1], #8 ldr data2, [src2], #8 L(start_realigned):
- subs limit_wd, limit_wd, #1
- subs limit, limit, #8 sub tmp1, data1, zeroones orr tmp2, data1, #REP8_7f eor diff, data1, data2 /* Non-zero if differences found. */
- csinv endloop, diff, xzr, pl /* Last Dword or differences. */
- csinv endloop, diff, xzr, hi /* Last Dword or differences. */ bics has_nul, tmp1, tmp2 /* Non-zero if NUL terminator. */ ccmp endloop, #0, #0, eq b.eq L(loop_aligned) /* End of main loop */
- /* Not reached the limit, must have found the end or a diff. */
- tbz limit_wd, #63, L(not_limit)
- /* Limit % 8 == 0 => all bytes significant. */
- ands limit, limit, #7
- b.eq L(not_limit)
- lsl limit, limit, #3 /* Bits -> bytes. */
- mov mask, #~0
-#ifdef __AARCH64EB__
- lsr mask, mask, limit
+L(full_check): +#ifndef __AARCH64EB__
- orr syndrome, diff, has_nul
- add limit, limit, 8 /* Rewind limit to before last subs. */
+L(syndrome_check):
- /* Limit was reached. Check if the NUL byte or the difference
is before the limit. */- rev syndrome, syndrome
- rev data1, data1
- clz pos, syndrome
- rev data2, data2
- lsl data1, data1, pos
- cmp limit, pos, lsr #3
- lsl data2, data2, pos
- /* But we need to zero-extend (char is unsigned) the value and then
perform a signed 32-bit subtraction. */- lsr data1, data1, #56
- sub result, data1, data2, lsr #56
- csel result, result, xzr, hi
- ret #else
- lsl mask, mask, limit
-#endif
- /* Not reached the limit, must have found the end or a diff. */
- tbz limit, #63, L(not_limit)
- add tmp1, limit, 8
- cbz limit, L(not_limit)
- lsl limit, tmp1, #3 /* Bits -> bytes. */
- mov mask, #~0
- lsr mask, mask, limit bic data1, data1, mask bic data2, data2, mask
@@ -95,25 +121,6 @@ L(start_realigned): orr has_nul, has_nul, mask L(not_limit):
- orr syndrome, diff, has_nul
-#ifndef __AARCH64EB__
- rev syndrome, syndrome
- rev data1, data1
- /* The MS-non-zero bit of the syndrome marks either the first bit
that is different, or the top bit of the first zero byte.Shifting left now will bring the critical information into thetop bits. */- clz pos, syndrome
- rev data2, data2
- lsl data1, data1, pos
- lsl data2, data2, pos
- /* But we need to zero-extend (char is unsigned) the value and then
perform a signed 32-bit subtraction. */- lsr data1, data1, #56
- sub result, data1, data2, lsr #56
- ret
-#else /* For big-endian we cannot use the trick with the syndrome value as carry-propagation can corrupt the upper bits if the trailing bytes in the string contain 0x01. */ @@ -134,10 +141,11 @@ L(not_limit): rev has_nul, has_nul orr syndrome, diff, has_nul clz pos, syndrome
- /* The MS-non-zero bit of the syndrome marks either the first bit
that is different, or the top bit of the first zero byte.
- /* The most-significant-non-zero bit of the syndrome marks either the
first bit that is different, or the top bit of the first zero byte. Shifting left now will bring the critical information into the top bits. */+L(end_quick): lsl data1, data1, pos lsl data2, data2, pos /* But we need to zero-extend (char is unsigned) the value and then @@ -159,22 +167,12 @@ L(mutual_align): neg tmp3, count, lsl #3 /* 64 - bits(bytes beyond align). */ ldr data2, [src2], #8 mov tmp2, #~0
- sub limit_wd, limit, #1 /* limit != 0, so no underflow. */
-#ifdef __AARCH64EB__
- /* Big-endian. Early bytes are at MSB. */
- lsl tmp2, tmp2, tmp3 /* Shift (count & 63). */
-#else
- /* Little-endian. Early bytes are at LSB. */
- lsr tmp2, tmp2, tmp3 /* Shift (count & 63). */
-#endif
- and tmp3, limit_wd, #7
- lsr limit_wd, limit_wd, #3
- /* Adjust the limit. Only low 3 bits used, so overflow irrelevant. */
- add limit, limit, count
- add tmp3, tmp3, count
- LS_FW tmp2, tmp2, tmp3 /* Shift (count & 63). */
- /* Adjust the limit and ensure it doesn't overflow. */
- adds limit, limit, count
- csinv limit, limit, xzr, lo orr data1, data1, tmp2 orr data2, data2, tmp2
- add limit_wd, limit_wd, tmp3, lsr #3 b L(start_realigned)
.p2align 4 @@ -197,13 +195,11 @@ L(done): /* Align the SRC1 to a dword by doing a bytewise compare and then do the dword loop. */ L(try_misaligned_words):
- lsr limit_wd, limit, #3
- cbz count, L(do_misaligned)
- cbz count, L(src1_aligned)
neg count, count and count, count, #7 sub limit, limit, count
- lsr limit_wd, limit, #3
L(page_end_loop): ldrb data1w, [src1], #1 @@ -214,48 +210,100 @@ L(page_end_loop): subs count, count, #1 b.hi L(page_end_loop) -L(do_misaligned):
- /* Prepare ourselves for the next page crossing. Unlike the aligned
loop, we fetch 1 less dword because we risk crossing bounds onSRC2. */- mov count, #8
- subs limit_wd, limit_wd, #1
- b.lo L(done_loop)
- /* The following diagram explains the comparison of misaligned strings.
The bytes are shown in natural order. For little-endian, it isreversed in the registers. The "x" bytes are before the string.The "|" separates data that is loaded at one time.src1 | a a a a a a a a | b b b c c c c c | . . .src2 | x x x x x a a a a a a a a b b b | c c c c c . . .After shifting in each step, the data looks like this:STEP_A STEP_B STEP_Cdata1 a a a a a a a a b b b c c c c c b b b c c c c cdata2 a a a a a a a a b b b 0 0 0 0 0 0 0 0 c c c c cThe bytes with "0" are eliminated from the syndrome via mask.Align SRC2 down to 16 bytes. This way we can read 16 bytes at atime from SRC2. The comparison happens in 3 steps. After each stepthe loop can exit, or read from SRC1 or SRC2. */+L(src1_aligned):
- /* Calculate offset from 8 byte alignment to string start in bits. No
need to mask offset since shifts are ignoring upper bits. */- lsl offset, src2, #3
- bic src2, src2, #0xf
- mov mask, -1
- neg neg_offset, offset
- ldr data1, [src1], #8
- ldp tmp1, tmp2, [src2], #16
- LS_BK mask, mask, neg_offset
- and neg_offset, neg_offset, #63 /* Need actual value for cmp later. */
- /* Skip the first compare if data in tmp1 is irrelevant. */
- tbnz offset, 6, L(misaligned_mid_loop)
- L(loop_misaligned):
- and tmp2, src2, #0xff8
- eor tmp2, tmp2, #0xff8
- cbz tmp2, L(page_end_loop)
- /* STEP_A: Compare full 8 bytes when there is enough data from SRC2.*/
- LS_FW data2, tmp1, offset
- LS_BK tmp1, tmp2, neg_offset
- subs limit, limit, #8
- orr data2, data2, tmp1 /* 8 bytes from SRC2 combined from two regs.*/
- sub has_nul, data1, zeroones
- eor diff, data1, data2 /* Non-zero if differences found. */
- orr tmp3, data1, #REP8_7f
- csinv endloop, diff, xzr, hi /* If limit, set to all ones. */
- bic has_nul, has_nul, tmp3 /* Non-zero if NUL byte found in SRC1. */
- orr tmp3, endloop, has_nul
- cbnz tmp3, L(full_check)
ldr data1, [src1], #8
- ldr data2, [src2], #8
- sub tmp1, data1, zeroones
- orr tmp2, data1, #REP8_7f
- eor diff, data1, data2 /* Non-zero if differences found. */
- bics has_nul, tmp1, tmp2 /* Non-zero if NUL terminator. */
- ccmp diff, #0, #0, eq
- b.ne L(not_limit)
- subs limit_wd, limit_wd, #1
- b.pl L(loop_misaligned)
+L(misaligned_mid_loop):
- /* STEP_B: Compare first part of data1 to second part of tmp2. */
- LS_FW data2, tmp2, offset
+#ifdef __AARCH64EB__
- /* For big-endian we do a byte reverse to avoid carry-propagation
- problem described above. This way we can reuse the has_nul in the
- next step and also use syndrome value trick at the end. */
- rev tmp3, data1
- #define data1_fixed tmp3
+#else
- #define data1_fixed data1
+#endif
- sub has_nul, data1_fixed, zeroones
- orr tmp3, data1_fixed, #REP8_7f
- eor diff, data2, data1 /* Non-zero if differences found. */
- bic has_nul, has_nul, tmp3 /* Non-zero if NUL terminator. */
+#ifdef __AARCH64EB__
- rev has_nul, has_nul
+#endif
- cmp limit, neg_offset, lsr #3
- orr syndrome, diff, has_nul
- bic syndrome, syndrome, mask /* Ignore later bytes. */
- csinv tmp3, syndrome, xzr, hi /* If limit, set to all ones. */
- cbnz tmp3, L(syndrome_check)
-L(done_loop):
- /* We found a difference or a NULL before the limit was reached. */
- and limit, limit, #7
- cbz limit, L(not_limit)
- /* Read the last word. */
- sub src1, src1, 8
- sub src2, src2, 8
- ldr data1, [src1, limit]
- ldr data2, [src2, limit]
- sub tmp1, data1, zeroones
- orr tmp2, data1, #REP8_7f
- eor diff, data1, data2 /* Non-zero if differences found. */
- bics has_nul, tmp1, tmp2 /* Non-zero if NUL terminator. */
- ccmp diff, #0, #0, eq
- b.ne L(not_limit)
- /* STEP_C: Compare second part of data1 to first part of tmp1. */
- ldp tmp1, tmp2, [src2], #16
- cmp limit, #8
- LS_BK data2, tmp1, neg_offset
- eor diff, data2, data1 /* Non-zero if differences found. */
- orr syndrome, diff, has_nul
- and syndrome, syndrome, mask /* Ignore earlier bytes. */
- csinv tmp3, syndrome, xzr, hi /* If limit, set to all ones. */
- cbnz tmp3, L(syndrome_check)
- ldr data1, [src1], #8
- sub limit, limit, #8
- b L(loop_misaligned)
+#ifdef __AARCH64EB__ +L(syndrome_check):
- clz pos, syndrome
- cmp pos, limit, lsl #3
- b.lo L(end_quick)
+#endif L(ret0): mov result, #0 ret
- SYM_FUNC_END_PI(strncmp) EXPORT_SYMBOL_NOHWKASAN(strncmp)