[PATCH v2 3/3] accel/tcg: Preserve PAGE_ANON when changing page permissions

[Richard Henderson]

Using mprotect() to change PROT_* does not change the MAP_ANON
previously set with mmap().  Our linux-user version of MTE only
works with MAP_ANON pages, so losing PAGE_ANON caused MTE to
stop working.

Reported-by: Stephen Long <steplong@quicinc.com>
Signed-off-by: Richard Henderson <richard.henderson@linaro.org>
---
 tests/tcg/aarch64/mte.h           |  3 ++-
 accel/tcg/translate-all.c         |  9 +++++--
 tests/tcg/aarch64/mte-6.c         | 43 +++++++++++++++++++++++++++++++
 tests/tcg/aarch64/Makefile.target |  2 +-
 4 files changed, 53 insertions(+), 4 deletions(-)
 create mode 100644 tests/tcg/aarch64/mte-6.c

diff --git a/tests/tcg/aarch64/mte.h b/tests/tcg/aarch64/mte.h
index 141cef522c..0805676b11 100644
--- a/tests/tcg/aarch64/mte.h
+++ b/tests/tcg/aarch64/mte.h
@@ -48,7 +48,8 @@ static void enable_mte(int tcf)
     }
 }
 
-static void *alloc_mte_mem(size_t size)
+static void * alloc_mte_mem(size_t size) __attribute__((unused));
+static void * alloc_mte_mem(size_t size)
 {
     void *p = mmap(NULL, size, PROT_READ | PROT_WRITE | PROT_MTE,
                    MAP_PRIVATE | MAP_ANONYMOUS, -1, 0);
diff --git a/accel/tcg/translate-all.c b/accel/tcg/translate-all.c
index f32df8b240..ba6ab09790 100644
--- a/accel/tcg/translate-all.c
+++ b/accel/tcg/translate-all.c
@@ -2714,6 +2714,8 @@ void page_set_flags(target_ulong start, target_ulong end, 
int flags)
        a missing call to h2g_valid.  */
     assert(end - 1 <= GUEST_ADDR_MAX);
     assert(start < end);
+    /* Only set PAGE_ANON with new mappings. */
+    assert(!(flags & PAGE_ANON) || (flags & PAGE_RESET));
     assert_memory_lock();
 
     start = start & TARGET_PAGE_MASK;
@@ -2737,11 +2739,14 @@ void page_set_flags(target_ulong start, target_ulong 
end, int flags)
             p->first_tb) {
             tb_invalidate_phys_page(addr, 0);
         }
-        if (reset_target_data && p->target_data) {
+        if (reset_target_data) {
             g_free(p->target_data);
             p->target_data = NULL;
+            p->flags = flags;
+        } else {
+            /* Using mprotect on a page does not change MAP_ANON. */
+            p->flags = (p->flags & PAGE_ANON) | flags;
         }
-        p->flags = flags;
     }
 }
 
diff --git a/tests/tcg/aarch64/mte-6.c b/tests/tcg/aarch64/mte-6.c
new file mode 100644
index 0000000000..60d51d18be
--- /dev/null
+++ b/tests/tcg/aarch64/mte-6.c
@@ -0,0 +1,43 @@
+#include "mte.h"
+
+void pass(int sig, siginfo_t *info, void *uc)
+{
+    assert(info->si_code == SEGV_MTESERR);
+    exit(0);
+}
+
+int main(void)
+{
+    enable_mte(PR_MTE_TCF_SYNC);
+
+    void *brk = sbrk(16);
+    if (brk == (void *)-1) {
+        perror("sbrk");
+        return 2;
+    }
+
+    if (mprotect(brk, 16, PROT_READ | PROT_WRITE | PROT_MTE)) {
+        perror("mprotect");
+        return 2;
+    }
+
+    int *p1, *p2;
+    long excl = 1;
+
+    asm("irg %0,%1,%2" : "=r"(p1) : "r"(brk), "r"(excl));
+    asm("gmi %0,%1,%0" : "+r"(excl) : "r"(p1));
+    asm("irg %0,%1,%2" : "=r"(p2) : "r"(brk), "r"(excl));
+    asm("stg %0,[%0]" : : "r"(p1));
+
+    *p1 = 0;
+
+    struct sigaction sa;
+    memset(&sa, 0, sizeof(sa));
+    sa.sa_sigaction = pass;
+    sa.sa_flags = SA_SIGINFO;
+    sigaction(SIGSEGV, &sa, NULL);
+
+    *p2 = 0;
+
+    abort();
+}
diff --git a/tests/tcg/aarch64/Makefile.target 
b/tests/tcg/aarch64/Makefile.target
index 6c95dd8b9e..928357b10a 100644
--- a/tests/tcg/aarch64/Makefile.target
+++ b/tests/tcg/aarch64/Makefile.target
@@ -37,7 +37,7 @@ AARCH64_TESTS += bti-2
 
 # MTE Tests
 ifneq ($(DOCKER_IMAGE)$(CROSS_CC_HAS_ARMV8_MTE),)
-AARCH64_TESTS += mte-1 mte-2 mte-3 mte-4 mte-5
+AARCH64_TESTS += mte-1 mte-2 mte-3 mte-4 mte-5 mte-6
 mte-%: CFLAGS += -march=armv8.5-a+memtag
 endif
 
-- 
2.25.1