From: Richard Henderson <richard.henderson@linaro.org>
To: "Alex Bennée" <alex.bennee@linaro.org>
Cc: qemu-devel@nongnu.org
Subject: Re: [PATCH v3 27/28] tcg: When allocating for !splitwx, begin with PROT_NONE
Date: Thu, 10 Jun 2021 08:34:21 -0700 [thread overview]
Message-ID: <06701a18-1702-618c-9495-2c43e2eff2d5@linaro.org> (raw)
In-Reply-To: <875yynjn72.fsf@linaro.org>
On 6/9/21 4:21 AM, Alex Bennée wrote:
>
> 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.
The comment *has* been updated: work with the page protections set up with the
initial mapping. Which is *not* always PROT_NONE.
See the USE_STATIC_CODE_GEN_BUFFER and _WIN32 copies of alloc_code_gen_buffer.
>> 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?
No.
r~
next prev parent reply other threads:[~2021-06-10 15:35 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
2021-06-10 15:34 ` Richard Henderson [this message]
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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