3 files changed, 85 insertions, 0 deletions
diff --git a/sysdeps/unix/sysv/linux/arm/be/libc.abilist b/sysdeps/unix/sysv/linux/arm/be/libc.abilist
index 573eca117e..f7a61fc73a 100644
--- a/sysdeps/unix/sysv/linux/arm/be/libc.abilist
+++ b/sysdeps/unix/sysv/linux/arm/be/libc.abilist
@@ -133,6 +133,7 @@ GLIBC_2.30 twalk_r F
 GLIBC_2.31 msgctl F
 GLIBC_2.31 semctl F
 GLIBC_2.31 shmctl F
+GLIBC_2.32 __rseq_abi T 0x20
 GLIBC_2.32 pthread_attr_getsigmask_np F
 GLIBC_2.32 pthread_attr_setaffinity_np F
 GLIBC_2.32 pthread_attr_setsigmask_np F
diff --git a/sysdeps/unix/sysv/linux/arm/bits/rseq.h b/sysdeps/unix/sysv/linux/arm/bits/rseq.h
new file mode 100644
index 0000000000..2bf780efcd
--- /dev/null
+++ b/sysdeps/unix/sysv/linux/arm/bits/rseq.h
@@ -0,0 +1,83 @@
+/* Restartable Sequences Linux arm architecture header.
+   Copyright (C) 2020 Free Software Foundation, Inc.
+
+   The GNU C Library is free software; you can redistribute it and/or
+   modify it under the terms of the GNU Lesser General Public
+   License as published by the Free Software Foundation; either
+   version 2.1 of the License, or (at your option) any later version.
+
+   The GNU C Library is distributed in the hope that it will be useful,
+   but WITHOUT ANY WARRANTY; without even the implied warranty of
+   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+   Lesser General Public License for more details.
+
+   You should have received a copy of the GNU Lesser General Public
+   License along with the GNU C Library; if not, see
+   <https://www.gnu.org/licenses/>.  */
+
+#ifndef _SYS_RSEQ_H
+# error "Never use <bits/rseq.h> directly; include <sys/rseq.h> instead."
+#endif
+
+/*
+   RSEQ_SIG is a signature required before each abort handler code.
+
+   It is a 32-bit value that maps to actual architecture code compiled
+   into applications and libraries.  It needs to be defined for each
+   architecture.  When choosing this value, it needs to be taken into
+   account that generating invalid instructions may have ill effects on
+   tools like objdump, and may also have impact on the CPU speculative
+   execution efficiency in some cases.
+
+   - ARM little endian
+
+   RSEQ_SIG uses the udf A32 instruction with an uncommon immediate operand
+   value 0x5de3.  This traps if user-space reaches this instruction by mistake,
+   and the uncommon operand ensures the kernel does not move the instruction
+   pointer to attacker-controlled code on rseq abort.
+
+   The instruction pattern in the A32 instruction set is:
+
+   e7f5def3    udf    #24035    ; 0x5de3
+
+   This translates to the following instruction pattern in the T16 instruction
+   set:
+
+   little endian:
+   def3        udf    #243      ; 0xf3
+   e7f5        b.n    <7f5>
+
+   - ARMv6+ big endian (BE8):
+
+   ARMv6+ -mbig-endian generates mixed endianness code vs data: little-endian
+   code and big-endian data.  The data value of the signature needs to have its
+   byte order reversed to generate the trap instruction:
+
+   Data: 0xf3def5e7
+
+   Translates to this A32 instruction pattern:
+
+   e7f5def3    udf    #24035    ; 0x5de3
+
+   Translates to this T16 instruction pattern:
+
+   def3        udf    #243      ; 0xf3
+   e7f5        b.n    <7f5>
+
+   - Prior to ARMv6 big endian (BE32):
+
+   Prior to ARMv6, -mbig-endian generates big-endian code and data
+   (which match), so the endianness of the data representation of the
+   signature should not be reversed.  However, the choice between BE32
+   and BE8 is done by the linker, so we cannot know whether code and
+   data endianness will be mixed before the linker is invoked.  So rather
+   than try to play tricks with the linker, the rseq signature is simply
+   data (not a trap instruction) prior to ARMv6 on big endian.  This is
+   why the signature is expressed as data (.word) rather than as
+   instruction (.inst) in assembler.  */
+
+#ifdef __ARMEB__
+# define RSEQ_SIG    0xf3def5e7      /* udf    #24035    ; 0x5de3 (ARMv6+) */
+#else
+# define RSEQ_SIG    0xe7f5def3      /* udf    #24035    ; 0x5de3 */
+#endif
diff --git a/sysdeps/unix/sysv/linux/arm/le/libc.abilist b/sysdeps/unix/sysv/linux/arm/le/libc.abilist
index 8a8633f0a4..c84ab6e5c3 100644
--- a/sysdeps/unix/sysv/linux/arm/le/libc.abilist
+++ b/sysdeps/unix/sysv/linux/arm/le/libc.abilist
@@ -130,6 +130,7 @@ GLIBC_2.30 getdents64 F
 GLIBC_2.30 gettid F
 GLIBC_2.30 tgkill F
 GLIBC_2.30 twalk_r F
+GLIBC_2.32 __rseq_abi T 0x20
 GLIBC_2.32 pthread_attr_getsigmask_np F
 GLIBC_2.32 pthread_attr_setaffinity_np F
 GLIBC_2.32 pthread_attr_setsigmask_np F