another tst-arm-mte bug: qemu-system segfaults

[Szabolcs Nagy <szabolcs.nagy@arm.com>]

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again i'm using the branch at

https://github.com/rth7680/qemu/tree/tgt-arm-mte

to test armv8.5-a mte, now qemu-system-aarch64 segfaults
and it's easy to reproduce: minimal source and static
linked binary is attached (should be executed on linux
with mte support, i used mte-v4 kernel with reverted
memory property check).

the __aarch64_memchr function referenced is from
https://github.com/ARM-software/optimized-routines

and the bug was originally observed when running the
test executables built with gcc-10 and a config.mk like

SUBS = string
ARCH = aarch64
srcdir = .
CROSS_COMPILE = aarch64-none-linux-gnu-
CC = $(CROSS_COMPILE)gcc
CFLAGS = -std=c99 -pipe -O3
CFLAGS += -march=armv8.5-a+memtag -DWANT_MTE_TEST=1
CFLAGS += -Wall -Wno-missing-braces
CFLAGS += -Werror=implicit-function-declaration
CFLAGS += -g

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#include <stddef.h>
#include <sys/mman.h>
#include <sys/prctl.h>

void *__memchr_aarch64 (const void *, int, size_t);

#define PR_SET_TAGGED_ADDR_CTRL 55
#define PR_TAGGED_ADDR_ENABLE (1UL << 0)
#define PR_MTE_TCF_SHIFT 1
#define PR_MTE_TCF_SYNC (1UL << PR_MTE_TCF_SHIFT)
#define PR_MTE_TAG_SHIFT 3
#define PROT_MTE 0x20

int main (void)
{
  int r = prctl (PR_SET_TAGGED_ADDR_CTRL, PR_TAGGED_ADDR_ENABLE | PR_MTE_TCF_SYNC | (0xfffe << PR_MTE_TAG_SHIFT), 0, 0, 0);
  if (r < 0) return -1;
  char *s = mmap (NULL, 4096, PROT_READ | PROT_WRITE | PROT_MTE, MAP_PRIVATE | MAP_ANONYMOUS, -1, 0);
  if (s == MAP_FAILED) return -1;
  s[0] = 1;
  __memchr_aarch64(s, 1, 4096);
  return 0;
}

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