From: Dmitry Safonov <dsafonov@virtuozzo.com> To: Thomas Gleixner <tglx@linutronix.de> Cc: <linux-kernel@vger.kernel.org>, <0x7f454c46@gmail.com>, Ingo Molnar <mingo@redhat.com>, "H. Peter Anvin" <hpa@zytor.com>, Andy Lutomirski <luto@kernel.org>, Borislav Petkov <bp@suse.de>, <x86@kernel.org>, <linux-mm@kvack.org>, Cyrill Gorcunov <gorcunov@openvz.org>, "Kirill A. Shutemov" <kirill.shutemov@linux.intel.com> Subject: Re: [PATCHv6 4/5] x86/mm: check in_compat_syscall() instead TIF_ADDR32 for mmap(MAP_32BIT) Date: Mon, 13 Mar 2017 12:56:18 +0300 [thread overview] Message-ID: <35a16a2c-c799-fe0c-2689-bf105b508663@virtuozzo.com> (raw) In-Reply-To: <alpine.DEB.2.20.1703131035020.3558@nanos> On 03/13/2017 12:39 PM, Thomas Gleixner wrote: > On Mon, 6 Mar 2017, Dmitry Safonov wrote: > >> Result of mmap() calls with MAP_32BIT flag at this moment depends >> on thread flag TIF_ADDR32, which is set during exec() for 32-bit apps. >> It's broken as the behavior of mmap() shouldn't depend on exec-ed >> application's bitness. Instead, it should check the bitness of mmap() >> syscall. >> How it worked before: >> o for 32-bit compatible binaries it is completely ignored. Which was >> fine when there were one mmap_base, computed for 32-bit syscalls. >> After introducing mmap_compat_base 64-bit syscalls do use computed >> for 64-bit syscalls mmap_base, which means that we can allocate 64-bit >> address with 64-bit syscall in application launched from 32-bit >> compatible binary. And ignoring this flag is not expected behavior. > > Well, the real question here is, whether we should allow 32bit applications > to obtain 64bit mappings at all. We can very well force 32bit applications > into the 4GB address space as it was before your mmap base splitup and be > done with it. Hmm, yes, we could restrict 32bit applications to 32bit mappings only. But the approach which I tried to follow in the patches set, it was do not base the logic on the bitness of launched applications (native/compat) - only base on bitness of the performing syscall. The idea was suggested by Andy and I made mmap() logic here independent from original application's bitness. It also seems to me simpler: if 32-bit application wants to allocate 64-bit mapping, it should long-jump with 64-bit segment descriptor and do `syscall` instruction for 64-bit syscall entry path. So, in my point of view after this dance the application does not differ much from native 64-bit binary and can have 64-bit address mapping. > > Thanks, > > tglx > > -- Dmitry
WARNING: multiple messages have this Message-ID (diff)
From: Dmitry Safonov <dsafonov@virtuozzo.com> To: Thomas Gleixner <tglx@linutronix.de> Cc: linux-kernel@vger.kernel.org, 0x7f454c46@gmail.com, Ingo Molnar <mingo@redhat.com>, "H. Peter Anvin" <hpa@zytor.com>, Andy Lutomirski <luto@kernel.org>, Borislav Petkov <bp@suse.de>, x86@kernel.org, linux-mm@kvack.org, Cyrill Gorcunov <gorcunov@openvz.org>, "Kirill A. Shutemov" <kirill.shutemov@linux.intel.com> Subject: Re: [PATCHv6 4/5] x86/mm: check in_compat_syscall() instead TIF_ADDR32 for mmap(MAP_32BIT) Date: Mon, 13 Mar 2017 12:56:18 +0300 [thread overview] Message-ID: <35a16a2c-c799-fe0c-2689-bf105b508663@virtuozzo.com> (raw) In-Reply-To: <alpine.DEB.2.20.1703131035020.3558@nanos> On 03/13/2017 12:39 PM, Thomas Gleixner wrote: > On Mon, 6 Mar 2017, Dmitry Safonov wrote: > >> Result of mmap() calls with MAP_32BIT flag at this moment depends >> on thread flag TIF_ADDR32, which is set during exec() for 32-bit apps. >> It's broken as the behavior of mmap() shouldn't depend on exec-ed >> application's bitness. Instead, it should check the bitness of mmap() >> syscall. >> How it worked before: >> o for 32-bit compatible binaries it is completely ignored. Which was >> fine when there were one mmap_base, computed for 32-bit syscalls. >> After introducing mmap_compat_base 64-bit syscalls do use computed >> for 64-bit syscalls mmap_base, which means that we can allocate 64-bit >> address with 64-bit syscall in application launched from 32-bit >> compatible binary. And ignoring this flag is not expected behavior. > > Well, the real question here is, whether we should allow 32bit applications > to obtain 64bit mappings at all. We can very well force 32bit applications > into the 4GB address space as it was before your mmap base splitup and be > done with it. Hmm, yes, we could restrict 32bit applications to 32bit mappings only. But the approach which I tried to follow in the patches set, it was do not base the logic on the bitness of launched applications (native/compat) - only base on bitness of the performing syscall. The idea was suggested by Andy and I made mmap() logic here independent from original application's bitness. It also seems to me simpler: if 32-bit application wants to allocate 64-bit mapping, it should long-jump with 64-bit segment descriptor and do `syscall` instruction for 64-bit syscall entry path. So, in my point of view after this dance the application does not differ much from native 64-bit binary and can have 64-bit address mapping. > > Thanks, > > tglx > > -- Dmitry -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@kvack.org. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: <a href=mailto:"dont@kvack.org"> email@kvack.org </a>
next prev parent reply other threads:[~2017-03-13 10:00 UTC|newest] Thread overview: 33+ messages / expand[flat|nested] mbox.gz Atom feed top 2017-03-06 14:17 [PATCHv6 0/5] Fix compatible mmap() return pointer over 4Gb Dmitry Safonov 2017-03-06 14:17 ` Dmitry Safonov 2017-03-06 14:17 ` [PATCHv6 1/5] x86/mm: introduce arch_rnd() to compute 32/64 mmap rnd Dmitry Safonov 2017-03-06 14:17 ` Dmitry Safonov 2017-03-13 14:03 ` [tip:x86/mm] x86/mm: Introduce arch_rnd() to compute 32/64 mmap random base tip-bot for Dmitry Safonov 2017-03-06 14:17 ` [PATCHv6 2/5] x86/mm: add task_size parameter to mmap_base() Dmitry Safonov 2017-03-06 14:17 ` Dmitry Safonov 2017-03-13 14:04 ` [tip:x86/mm] x86/mm: Add " tip-bot for Dmitry Safonov 2017-03-06 14:17 ` [PATCHv6 3/5] x86/mm: introduce mmap_compat_base for 32-bit mmap() Dmitry Safonov 2017-03-06 14:17 ` Dmitry Safonov 2017-03-13 14:04 ` [tip:x86/mm] x86/mm: Introduce mmap_compat_base() " tip-bot for Dmitry Safonov 2017-03-14 1:30 ` [lkp-robot] [x86/mm] 0d708eaade: libhugetlbfs.32bit.unlinked_fd.fail kernel test robot 2017-03-14 1:30 ` kernel test robot 2017-03-14 1:30 ` kernel test robot 2017-03-06 14:17 ` [PATCHv6 4/5] x86/mm: check in_compat_syscall() instead TIF_ADDR32 for mmap(MAP_32BIT) Dmitry Safonov 2017-03-06 14:17 ` Dmitry Safonov 2017-03-13 9:39 ` Thomas Gleixner 2017-03-13 9:39 ` Thomas Gleixner 2017-03-13 9:56 ` Dmitry Safonov [this message] 2017-03-13 9:56 ` Dmitry Safonov 2017-03-13 13:47 ` Thomas Gleixner 2017-03-13 13:47 ` Thomas Gleixner 2017-03-13 13:56 ` Dmitry Safonov 2017-03-13 13:56 ` Dmitry Safonov 2017-03-13 14:03 ` Thomas Gleixner 2017-03-13 14:03 ` Thomas Gleixner 2017-03-13 14:17 ` Dmitry Safonov 2017-03-13 14:17 ` Dmitry Safonov 2017-03-13 15:29 ` Andy Lutomirski 2017-03-13 15:29 ` Andy Lutomirski 2017-03-13 14:05 ` [tip:x86/mm] x86/mm: Make mmap(MAP_32BIT) work correctly tip-bot for Dmitry Safonov 2017-03-06 14:17 ` [PATCHv6 5/5] selftests/x86: add test for 32-bit mmap() return addr Dmitry Safonov 2017-03-06 14:17 ` Dmitry Safonov
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