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Date: Tue, 14 Feb 2017 19:11:40 +0300 From: Dmitry Safonov <dsafonov@...tuozzo.com> To: Thomas Gleixner <tglx@...utronix.de> CC: <linux-kernel@...r.kernel.org>, <0x7f454c46@...il.com>, Ingo Molnar <mingo@...hat.com>, "H. Peter Anvin" <hpa@...or.com>, Andy Lutomirski <luto@...nel.org>, Borislav Petkov <bp@...e.de>, <x86@...nel.org>, <linux-mm@...ck.org> Subject: Re: [PATCHv4 4/5] x86/mm: check in_compat_syscall() instead TIF_ADDR32 for mmap(MAP_32BIT) On 02/11/2017 11:13 PM, Thomas Gleixner wrote: > On Mon, 30 Jan 2017, Dmitry Safonov wrote: > >> At this momet, logic in arch_get_unmapped_area{,_topdown} for mmaps with >> MAP_32BIT flag checks TIF_ADDR32 which means: >> o if 32-bit ELF changes mode to 64-bit on x86_64 and then tries to >> mmap() with MAP_32BIT it'll result in addr over 4Gb (as default is >> top-down allocation) >> o if 64-bit ELF changes mode to 32-bit and tries mmap() with MAP_32BIT, >> it'll allocate only memory in 1GB space: [0x40000000, 0x80000000). >> >> Fix it by handeling MAP_32BIT in 64-bit syscalls only. > > I really have a hard time to understand what is fixed and how that is > related to the $subject. > > Again. Please explain the problem first properly so one can understand the > issue immediately. Ok, rewrote the changes log. > >> As a little bonus it'll make thread flag a little less used. > > I really do not understand the bonus part here. You replace the thread flag > check with a different one and AFAICT this looks like oart of the 'fix'. It's a part of the fix, right. What I meant here is that after those patches TIF_ADDR32 is no more used after exec() time. That's bonus as if we manage to change exec() code in some way (i.e., pass address restriction as a parameter), we'll have additional free thread info flag. > Thanks, > > tglx > >> @@ -101,7 +101,7 @@ SYSCALL_DEFINE6(mmap, unsigned long, addr, unsigned long, len, >> static void find_start_end(unsigned long flags, unsigned long *begin, >> unsigned long *end) >> { >> - if (!test_thread_flag(TIF_ADDR32) && (flags & MAP_32BIT)) { >> + if (!in_compat_syscall() && (flags & MAP_32BIT)) { >> /* This is usually used needed to map code in small >> model, so it needs to be in the first 31bit. Limit >> it to that. This means we need to move the >> @@ -195,7 +195,7 @@ arch_get_unmapped_area_topdown(struct file *filp, const unsigned long addr0, >> return addr; >> >> /* for MAP_32BIT mappings we force the legacy mmap base */ >> - if (!test_thread_flag(TIF_ADDR32) && (flags & MAP_32BIT)) >> + if (!in_compat_syscall() && (flags & MAP_32BIT)) >> goto bottomup; >> >> /* requesting a specific address */ >> -- >> 2.11.0 >> >> -- Dmitry
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