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[PATCH v2 28/29] tcg: When allocating for !splitwx, begin with PROT_NONE
From: |
Richard Henderson |
Subject: |
[PATCH v2 28/29] tcg: When allocating for !splitwx, begin with PROT_NONE |
Date: |
Sun, 14 Mar 2021 15:27:23 -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 fac416ebf5..53f78965c7 100644
--- a/tcg/region.c
+++ b/tcg/region.c
@@ -765,12 +765,15 @@ 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 v2 14/29] tcg: Introduce tcg_max_ctxs, (continued)
- [PATCH v2 14/29] tcg: Introduce tcg_max_ctxs, Richard Henderson, 2021/03/14
- [PATCH v2 15/29] tcg: Move MAX_CODE_GEN_BUFFER_SIZE to tcg-target.h, Richard Henderson, 2021/03/14
- [PATCH v2 16/29] tcg: Replace region.end with region.total_size, Richard Henderson, 2021/03/14
- [PATCH v2 20/29] tcg: Move in_code_gen_buffer and tests to region.c, Richard Henderson, 2021/03/14
- [PATCH v2 17/29] tcg: Rename region.start to region.after_prologue, Richard Henderson, 2021/03/14
- [PATCH v2 19/29] tcg: Tidy split_cross_256mb, Richard Henderson, 2021/03/14
- [PATCH v2 18/29] tcg: Tidy tcg_n_regions, Richard Henderson, 2021/03/14
- [PATCH v2 23/29] tcg: Sink qemu_madvise call to common code, Richard Henderson, 2021/03/14
- [PATCH v2 26/29] tcg: Round the tb_size default from qemu_get_host_physmem, Richard Henderson, 2021/03/14
- [PATCH v2 24/29] tcg: Do not set guard pages in the rx buffer, Richard Henderson, 2021/03/14
- [PATCH v2 28/29] tcg: When allocating for !splitwx, begin with PROT_NONE,
Richard Henderson <=
- [PATCH v2 29/29] tcg: Move tcg_init_ctx and tcg_ctx from accel/tcg/, Richard Henderson, 2021/03/14
- [PATCH v2 25/29] util/osdep: Add qemu_mprotect_rw, Richard Henderson, 2021/03/14
- [PATCH v2 21/29] tcg: Allocate code_gen_buffer into struct tcg_region_state, Richard Henderson, 2021/03/14
- [PATCH v2 27/29] tcg: Merge buffer protection and guard page protection, Richard Henderson, 2021/03/14
- [PATCH v2 22/29] tcg: Return the map protection from alloc_code_gen_buffer, Richard Henderson, 2021/03/14
- Re: [PATCH v2 00/29] tcg: Workaround macOS 11.2 mprotect bug, no-reply, 2021/03/14
- Re: [PATCH v2 00/29] tcg: Workaround macOS 11.2 mprotect bug, Roman Bolshakov, 2021/03/15