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Subject: Re: [PATCH RESEND 2/2] x86/mm: Randomize va with generic
 arch_pick_mmap_layout()
From:   Xiongwei Song <sxwjean@me.com>
In-Reply-To: <YUnvKV0Qf6zhiasz@hirez.programming.kicks-ass.net>
Date:   Wed, 22 Sep 2021 21:28:36 +0800
Cc:     x86@kernel.org, linux-mm@kvack.org,
        Thomas Gleixner <tglx@linutronix.de>,
        Ingo Molnar <mingo@redhat.com>, Borislav Petkov <bp@alien8.de>,
        "H. Peter Anvin" <hpa@zytor.com>,
        Andy Lutomirski <luto@kernel.org>,
        Gabriel Krisman Bertazi <krisman@collabora.com>,
        "Chang S. Bae" <chang.seok.bae@intel.com>,
        Al Viro <viro@zeniv.linux.org.uk>,
        Arvind Sankar <nivedita@alum.mit.edu>, adobriyan@gmail.com,
        oleg@redhat.com, sblbir@amazon.com, axboe@kernel.dk,
        laijs@linux.alibaba.com, dave.hansen@linux.intel.com,
        akpm@linux-foundation.org, arnd@arndb.de, davem@davemloft.net,
        keescook@chromium.org, kim.phillips@amd.com, yazen.ghannam@amd.com,
        dave@stgolabs.net, metze@samba.org, elver@google.com,
        ebiederm@xmission.com, christophe.leroy@csgroup.eu,
        linux-kernel@vger.kernel.org, Xiongwei Song <sxwjean@gmail.com>
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References: <20210921143414.70723-1-sxwjean@me.com>
 <20210921143414.70723-3-sxwjean@me.com>
 <YUnvKV0Qf6zhiasz@hirez.programming.kicks-ass.net>
To:     Peter Zijlstra <peterz@infradead.org>
Precedence: bulk


> On Sep 21, 2021, at 10:41 PM, Peter Zijlstra <peterz@infradead.org> =
wrote:
>=20
> On Tue, Sep 21, 2021 at 10:34:14PM +0800, sxwjean@me.com wrote:
>> diff --git a/arch/x86/include/asm/compat.h =
b/arch/x86/include/asm/compat.h
>> index 7516e4199b3c..c697e377644d 100644
>> --- a/arch/x86/include/asm/compat.h
>> +++ b/arch/x86/include/asm/compat.h
>> @@ -151,6 +151,11 @@ struct compat_shmid64_ds {
>> 	compat_ulong_t __unused5;
>> };
>>=20
>> +static inline int is_compat_task(void)
>> +{
>> +	return IS_ENABLED(CONFIG_COMPAT) && test_thread_flag(TIF_32BIT);
>> +}
>> +
>=20
> This is still fundamentally broken for x86. x86 doesn't have compat
> tasks, the granularity is at syscall at best.

Hi Peter,

Thank you for pointing this out. I understand now a 64bit task can call =
a 32bit syscall.=20
Here we should use in_compat_syscall() to check if the kernel is in =
compat mode, right?

Regards,
Xiongwei=