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.
> 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'.
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
>
>
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