[v2,5/6] aarch64: Add sysv specific enabling code for memory tagging
Commit Message
Add various defines and stubs for enabling MTE on AArch64 sysv-like
systems such as Linux. The HWCAP feature bit is copied over in the
same way as other feature bits. Similarly we add a new wrapper header
for mman.h to define the PROT_MTE flag that can be used with mmap and
related functions.
We add a new field to struct cpu_features that can be used, for
example, to check whether or not certain ifunc'd routines should be
bound to MTE-safe versions.
Finally, if we detect that MTE should be enabled (ie via the glibc
tunable); we enable MTE during startup as required.
---
sysdeps/unix/sysv/linux/aarch64/bits/hwcap.h | 1 +
sysdeps/unix/sysv/linux/aarch64/bits/mman.h | 32 +++++++++++++++++++
.../unix/sysv/linux/aarch64/cpu-features.c | 28 ++++++++++++++++
.../unix/sysv/linux/aarch64/cpu-features.h | 1 +
4 files changed, 62 insertions(+)
create mode 100644 sysdeps/unix/sysv/linux/aarch64/bits/mman.h
@@ -72,3 +72,4 @@
#define HWCAP2_BF16 (1 << 14)
#define HWCAP2_DGH (1 << 15)
#define HWCAP2_RNG (1 << 16)
+#define HWCAP2_MTE (1 << 18)
new file mode 100644
@@ -0,0 +1,32 @@
+/* Definitions for POSIX memory map interface. Linux/aarch64 version.
+ Copyright (C) 2020 Free Software Foundation, Inc.
+ This file is part of the GNU C Library.
+
+ 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_MMAN_H
+# error "Never use <bits/mman.h> directly; include <sys/mman.h> instead."
+#endif
+
+/* The following definitions basically come from the kernel headers.
+ But the kernel header is not namespace clean. */
+
+/* Other flags. */
+#define PROT_MTE 0x20 /* Normal Tagged mapping. */
+
+#include <bits/mman-map-flags-generic.h>
+
+/* Include generic Linux declarations. */
+#include <bits/mman-linux.h>
@@ -19,6 +19,7 @@
#include <cpu-features.h>
#include <sys/auxv.h>
#include <elf/dl-hwcaps.h>
+#include <sys/prctl.h>
#define DCZID_DZP_MASK (1 << 4)
#define DCZID_BS_MASK (0xf)
@@ -83,4 +84,31 @@ init_cpu_features (struct cpu_features *cpu_features)
if ((dczid & DCZID_DZP_MASK) == 0)
cpu_features->zva_size = 4 << (dczid & DCZID_BS_MASK);
+
+ /* Setup memory tagging support if the HW and kernel support it, and if
+ the user has requested it. */
+ cpu_features->mte_state = 0;
+
+#ifdef _LIBC_MTAG
+# if HAVE_TUNABLES
+ int mte_state = TUNABLE_GET (glibc, memtag, enable, unsigned, 0);
+ cpu_features->mte_state = (GLRO (dl_hwcap2) & HWCAP2_MTE) ? mte_state : 0;
+ /* If we lack the MTE feature, disable the tunable, since it will
+ otherwise cause instructions that won't run on this CPU to be used. */
+ TUNABLE_SET (glibc, memtag, enable, unsigned, cpu_features->mte_state);
+# endif
+
+ /* For now, disallow tag 0, so that we can clearly see when tagged
+ addresses are being allocated. */
+ if (cpu_features->mte_state & 2)
+ __prctl (PR_SET_TAGGED_ADDR_CTRL,
+ (PR_TAGGED_ADDR_ENABLE | PR_MTE_TCF_SYNC
+ | (0xfffe << PR_MTE_TAG_SHIFT)),
+ 0, 0, 0);
+ else if (cpu_features->mte_state)
+ __prctl (PR_SET_TAGGED_ADDR_CTRL,
+ (PR_TAGGED_ADDR_ENABLE | PR_MTE_TCF_ASYNC
+ | (0xfffe << PR_MTE_TAG_SHIFT)),
+ 0, 0, 0);
+#endif
}
@@ -64,6 +64,7 @@ struct cpu_features
{
uint64_t midr_el1;
unsigned zva_size;
+ unsigned mte_state;
};
#endif /* _CPU_FEATURES_AARCH64_H */