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[PATCH 26/26] tcg: When allocating for !splitwx, begin with PROT_NONE
From: |
Richard Henderson |
Subject: |
[PATCH 26/26] tcg: When allocating for !splitwx, begin with PROT_NONE |
Date: |
Wed, 10 Mar 2021 18:21:56 -0600 |
There's a change in mprotect() behaviour [1] in the latest macOS
on M1 and it's not yet clear if it's going to be fixed by Apple.
In this case, instead of changing permissions of N guard pages,
we change permissions of N rwx regions. The same number of
syscalls are required either way.
[1] https://gist.github.com/hikalium/75ae822466ee4da13cbbe486498a191f
Buglink: https://bugs.launchpad.net/qemu/+bug/1914849
Signed-off-by: Richard Henderson <richard.henderson@linaro.org>
---
tcg/region.c | 13 ++++++++-----
1 file changed, 8 insertions(+), 5 deletions(-)
diff --git a/tcg/region.c b/tcg/region.c
index 5b46172fb5..3ffea215a2 100644
--- a/tcg/region.c
+++ b/tcg/region.c
@@ -749,12 +749,15 @@ static int alloc_code_gen_buffer(size_t size, int
splitwx, Error **errp)
error_free_or_abort(errp);
}
- prot = PROT_READ | PROT_WRITE | PROT_EXEC;
+ /*
+ * macOS 11.2 has a bug (Apple Feedback FB8994773) in which mprotect
+ * rejects a permission change from RWX -> NONE when reserving the
+ * guard pages later. We can go the other way with the same number
+ * of syscalls, so always begin with PROT_NONE.
+ */
+ prot = PROT_NONE;
flags = MAP_PRIVATE | MAP_ANONYMOUS;
-#ifdef CONFIG_TCG_INTERPRETER
- /* The tcg interpreter does not need execute permission. */
- prot = PROT_READ | PROT_WRITE;
-#elif defined(CONFIG_DARWIN)
+#ifdef CONFIG_DARWIN
/* Applicable to both iOS and macOS (Apple Silicon). */
if (!splitwx) {
flags |= MAP_JIT;
--
2.25.1
- [PATCH 13/26] accel/tcg: Merge tcg_exec_init into tcg_init_machine, (continued)
- [PATCH 13/26] accel/tcg: Merge tcg_exec_init into tcg_init_machine, Richard Henderson, 2021/03/10
- [PATCH 23/26] tcg: Do not set guard pages in the rx buffer, Richard Henderson, 2021/03/10
- [PATCH 21/26] tcg: Return the map protection from alloc_code_gen_buffer, Richard Henderson, 2021/03/10
- [PATCH 20/26] tcg: Allocate code_gen_buffer into struct tcg_region_state, Richard Henderson, 2021/03/10
- [PATCH 22/26] tcg: Sink qemu_madvise call to common code, Richard Henderson, 2021/03/10
- [PATCH 15/26] tcg: Introduce tcg_max_ctxs, Richard Henderson, 2021/03/10
- [PATCH 25/26] tcg: Merge buffer protection and guard page protection, Richard Henderson, 2021/03/10
- [PATCH 24/26] util/osdep: Add qemu_mprotect_rw, Richard Henderson, 2021/03/10
- [PATCH 26/26] tcg: When allocating for !splitwx, begin with PROT_NONE,
Richard Henderson <=
- Re: [PATCH 00/26] tcg: Workaround macOS 11.2 mprotect bug, no-reply, 2021/03/10