Rasmus- I think you're right - I was not paying close enough attention. In this case, I think the real culprit appears to be something like libc incorrectly sign-extending the mmap() offset argument. Calling mmap() with an offset of 0xf80000000 is resulting in a pg_off of 0xffff8000 when the syscall wrappers convert the mmap() call to mmap_pgoff(). This is on MIPS linux - I'll dig further on the user side to see why the offset is being sign extended. The proper casts *seem* to be in place in libc, but its plainly not doing what it's supposed to. -reese
> -----Original Message----- > From: Rasmus Villemoes [mailto:[email protected]] > Sent: Friday, May 08, 2015 2:46 AM > To: Reese Faucette > Cc: [email protected]; [email protected] > Subject: Re: [PATCH] overflow check calculation in mm/mmap.c is incorrect > linux-3.12.38 > > On Thu, Apr 30 2015, "Reese Faucette" <[email protected]> wrote: > > > When checking for overflow, the code in mm/mmap.c compares the first > > byte > > *after* the end of mapped region to the start of the region instead of > > the last byte of the mapped region. This prevents mapping a region > > which abuts the end of physical space, as mmap() incorrectly rejects > > the region with -EOVERFLOW, because pgoff + (len >> PAGE_SHIFT) will > > be 0, which is < pgoff. > > Note this comment elsewhere in mmap.c: > > * We don't check here for the merged mmap wrapping around the end of > pagecache > * indices (16TB on ia32) because do_mmap_pgoff() does not permit mmap's > which > * wrap, nor mmaps which cover the final page at index -1UL. > > So it seems to be by design. > > But I'm also a little confused, since pgoff should be in units of pages (so a > 20 bit number on 32bit), and I can't see how adding another 20 bit number > could ever make that overflow. Unless of course some magic power ensures > that pgoffs in the high half get sign-extended. > > Rasmus -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to [email protected] More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
