diff options
| author | Richard Henderson <richard.henderson@linaro.org> | 2021-03-10 17:41:26 -0600 |
|---|---|---|
| committer | Richard Henderson <richard.henderson@linaro.org> | 2021-06-13 17:42:40 -0700 |
| commit | b7da02dad0f25928e688a5dce74a0f10fa120594 (patch) | |
| tree | 09f40a14d9d3018f4b32ad0e4ba561bc4b57587f /tcg/region.c | |
| parent | 22c6a9938f7515a2c05fb7dea128e2e305953115 (diff) | |
tcg: When allocating for !splitwx, begin with PROT_NONE
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
Reviewed-by: Luis Pires <luis.pires@eldorado.org.br>
Signed-off-by: Richard Henderson <richard.henderson@linaro.org>
Diffstat (limited to 'tcg/region.c')
| -rw-r--r-- | tcg/region.c | 19 |
1 files changed, 9 insertions, 10 deletions
diff --git a/tcg/region.c b/tcg/region.c index 42d3fa9ba1..00b0c3b091 100644 --- a/tcg/region.c +++ b/tcg/region.c @@ -770,12 +770,15 @@ 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; @@ -906,11 +909,7 @@ void tcg_region_init(size_t tb_size, int splitwx, unsigned max_cpus) } } if (have_prot != 0) { - /* - * macOS 11.2 has a bug (Apple Feedback FB8994773) in which mprotect - * rejects a permission change from RWX -> NONE. Guard pages are - * nice for bug detection but are not essential; ignore any failure. - */ + /* Guard pages are nice for bug detection but are not essential. */ (void)qemu_mprotect_none(end, page_size); } } |