From: "Alex Bennée" <alex.bennee@linaro.org>
To: Richard Henderson <richard.henderson@linaro.org>
Cc: qemu-devel@nongnu.org
Subject: Re: [PATCH v3 27/28] tcg: When allocating for !splitwx, begin with PROT_NONE
Date: Wed, 09 Jun 2021 12:21:16 +0100 [thread overview]
Message-ID: <875yynjn72.fsf@linaro.org> (raw)
In-Reply-To: <20210502231844.1977630-28-richard.henderson@linaro.org>
Richard Henderson <richard.henderson@linaro.org> writes:
> 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
>
> Signed-off-by: Richard Henderson <richard.henderson@linaro.org>
> ---
> tcg/region.c | 19 +++++++++----------
> 1 file changed, 9 insertions(+), 10 deletions(-)
>
> diff --git a/tcg/region.c b/tcg/region.c
> index 604530b902..5e00db4cfb 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;
> @@ -901,11 +904,7 @@ void tcg_region_init(size_t tb_size, int splitwx, unsigned max_cpus)
> }
> }
I think the comment in tcg_region_init needs to be updated, currently
reads:
/*
* Set guard pages in the rw buffer, as that's the one into which
* buffer overruns could occur. Do not set guard pages in the rx
* buffer -- let that one use hugepages throughout.
* Work with the page protections set up with the initial mapping.
*/
need_prot = PAGE_READ | PAGE_WRITE;
but now we start with everything at PROT_NONE and are just setting
need_prot for the non-guard pages.
> 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);
Isn't the last page already set as PROT_NONE?
> }
> }
--
Alex Bennée
next prev parent reply other threads:[~2021-06-09 11:24 UTC|newest]
Thread overview: 92+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-05-02 23:18 [PATCH v3 00/28] tcg: Clean up code_gen_buffer allocation Richard Henderson
2021-05-02 23:18 ` [PATCH v3 01/28] meson: Split out tcg/meson.build Richard Henderson
2021-06-07 19:38 ` Alex Bennée
2021-06-09 14:56 ` Luis Fernando Fujita Pires
2021-05-02 23:18 ` [PATCH v3 02/28] meson: Split out fpu/meson.build Richard Henderson
2021-06-07 19:38 ` Alex Bennée
2021-06-09 14:57 ` Luis Fernando Fujita Pires
2021-05-02 23:18 ` [PATCH v3 03/28] tcg: Re-order tcg_region_init vs tcg_prologue_init Richard Henderson
2021-06-08 9:04 ` Alex Bennée
2021-06-09 14:57 ` Luis Fernando Fujita Pires
2021-05-02 23:18 ` [PATCH v3 04/28] tcg: Remove error return from tcg_region_initial_alloc__locked Richard Henderson
2021-06-08 11:04 ` Alex Bennée
2021-06-08 15:44 ` Richard Henderson
2021-06-09 14:57 ` Luis Fernando Fujita Pires
2021-05-02 23:18 ` [PATCH v3 05/28] tcg: Split out tcg_region_initial_alloc Richard Henderson
2021-06-08 11:45 ` Alex Bennée
2021-06-09 14:57 ` Luis Fernando Fujita Pires
2021-05-02 23:18 ` [PATCH v3 06/28] tcg: Split out tcg_region_prologue_set Richard Henderson
2021-06-08 11:47 ` Alex Bennée
2021-06-09 14:57 ` Luis Fernando Fujita Pires
2021-05-02 23:18 ` [PATCH v3 07/28] tcg: Split out region.c Richard Henderson
2021-06-08 11:48 ` Alex Bennée
2021-06-09 14:57 ` Luis Fernando Fujita Pires
2021-05-02 23:18 ` [PATCH v3 08/28] accel/tcg: Inline cpu_gen_init Richard Henderson
2021-06-08 11:49 ` Alex Bennée
2021-06-09 14:57 ` Luis Fernando Fujita Pires
2021-05-02 23:18 ` [PATCH v3 09/28] accel/tcg: Move alloc_code_gen_buffer to tcg/region.c Richard Henderson
2021-06-08 11:50 ` Alex Bennée
2021-06-09 14:57 ` Luis Fernando Fujita Pires
2021-05-02 23:18 ` [PATCH v3 10/28] accel/tcg: Rename tcg_init to tcg_init_machine Richard Henderson
2021-06-08 11:51 ` Alex Bennée
2021-06-09 14:57 ` Luis Fernando Fujita Pires
2021-05-02 23:18 ` [PATCH v3 11/28] tcg: Create tcg_init Richard Henderson
2021-06-08 11:52 ` Alex Bennée
2021-06-09 14:57 ` Luis Fernando Fujita Pires
2021-05-02 23:18 ` [PATCH v3 12/28] accel/tcg: Merge tcg_exec_init into tcg_init_machine Richard Henderson
2021-06-08 11:55 ` Alex Bennée
2021-06-08 15:45 ` Richard Henderson
2021-06-09 14:58 ` Luis Fernando Fujita Pires
2021-06-10 15:16 ` Richard Henderson
2021-05-02 23:18 ` [PATCH v3 13/28] accel/tcg: Pass down max_cpus to tcg_init Richard Henderson
2021-06-08 15:44 ` Alex Bennée
2021-06-09 14:58 ` Luis Fernando Fujita Pires
2021-05-02 23:18 ` [PATCH v3 14/28] tcg: Introduce tcg_max_ctxs Richard Henderson
2021-06-08 15:54 ` Alex Bennée
2021-06-09 14:58 ` Luis Fernando Fujita Pires
2021-05-02 23:18 ` [PATCH v3 15/28] tcg: Move MAX_CODE_GEN_BUFFER_SIZE to tcg-target.h Richard Henderson
2021-06-08 15:56 ` Alex Bennée
2021-06-09 14:58 ` Luis Fernando Fujita Pires
2021-05-02 23:18 ` [PATCH v3 16/28] tcg: Replace region.end with region.total_size Richard Henderson
2021-06-08 16:03 ` Alex Bennée
2021-06-08 16:12 ` Richard Henderson
2021-06-09 14:58 ` Luis Fernando Fujita Pires
2021-05-02 23:18 ` [PATCH v3 17/28] tcg: Rename region.start to region.after_prologue Richard Henderson
2021-06-08 16:06 ` Alex Bennée
2021-06-09 14:58 ` Luis Fernando Fujita Pires
2021-05-02 23:18 ` [PATCH v3 18/28] tcg: Tidy tcg_n_regions Richard Henderson
2021-06-08 16:06 ` Alex Bennée
2021-06-09 14:58 ` Luis Fernando Fujita Pires
2021-05-02 23:18 ` [PATCH v3 19/28] tcg: Tidy split_cross_256mb Richard Henderson
2021-06-09 10:01 ` Alex Bennée
2021-06-09 14:59 ` Luis Fernando Fujita Pires
2021-06-10 15:20 ` Richard Henderson
2021-05-02 23:18 ` [PATCH v3 20/28] tcg: Move in_code_gen_buffer and tests to region.c Richard Henderson
2021-06-09 10:07 ` Alex Bennée
2021-06-09 14:59 ` Luis Fernando Fujita Pires
2021-05-02 23:18 ` [PATCH v3 21/28] tcg: Allocate code_gen_buffer into struct tcg_region_state Richard Henderson
2021-06-09 10:29 ` Alex Bennée
2021-06-09 14:59 ` Luis Fernando Fujita Pires
2021-05-02 23:18 ` [PATCH v3 22/28] tcg: Return the map protection from alloc_code_gen_buffer Richard Henderson
2021-06-09 10:30 ` Alex Bennée
2021-06-09 14:59 ` Luis Fernando Fujita Pires
2021-05-02 23:18 ` [PATCH v3 23/28] tcg: Sink qemu_madvise call to common code Richard Henderson
2021-06-09 10:34 ` Alex Bennée
2021-06-09 14:59 ` Luis Fernando Fujita Pires
2021-05-02 23:18 ` [PATCH v3 24/28] util/osdep: Add qemu_mprotect_rw Richard Henderson
2021-06-09 10:34 ` Alex Bennée
2021-06-09 14:59 ` Luis Fernando Fujita Pires
2021-05-02 23:18 ` [PATCH v3 25/28] tcg: Round the tb_size default from qemu_get_host_physmem Richard Henderson
2021-06-09 10:36 ` Alex Bennée
2021-06-09 14:59 ` Luis Fernando Fujita Pires
2021-05-02 23:18 ` [PATCH v3 26/28] tcg: Merge buffer protection and guard page protection Richard Henderson
2021-06-09 10:39 ` Alex Bennée
2021-06-09 14:59 ` Luis Fernando Fujita Pires
2021-05-02 23:18 ` [PATCH v3 27/28] tcg: When allocating for !splitwx, begin with PROT_NONE Richard Henderson
2021-06-09 11:21 ` Alex Bennée [this message]
2021-06-10 15:34 ` Richard Henderson
2021-06-09 14:59 ` Luis Fernando Fujita Pires
2021-05-02 23:18 ` [PATCH v3 28/28] tcg: Move tcg_init_ctx and tcg_ctx from accel/tcg/ Richard Henderson
2021-06-09 11:30 ` Alex Bennée
2021-06-09 14:59 ` Luis Fernando Fujita Pires
2021-05-02 23:45 ` [PATCH v3 00/28] tcg: Clean up code_gen_buffer allocation no-reply
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