Messages in this thread | | | Subject | Re: [PATCHv4 4/5] x86/mm: check in_compat_syscall() instead TIF_ADDR32 for mmap(MAP_32BIT) | From | Dmitry Safonov <> | Date | Tue, 14 Feb 2017 19:14:27 +0300 |
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On 02/14/2017 07:11 PM, Dmitry Safonov wrote: > 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.
Oh, I lied here: it'll be still used for TASK_SIZE macro and etc. But, I don't see why in generic code we can't use TASK_SIZE_MAX, at least at this moment.
> >> 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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