On March 21, 2017 2:16:48 PM PDT, Adam Borowski <kilobyte@xxxxxxxxxx> wrote: >On Tue, Mar 21, 2017 at 08:47:11PM +0300, Dmitry Safonov wrote: >> After my changes to mmap(), its code now relies on the bitness of >> performing syscall. According to that, it chooses the base of >allocation: >> mmap_base for 64-bit mmap() and mmap_compat_base for 32-bit syscall. >> It was done by: >> commit 1b028f784e8c ("x86/mm: Introduce mmap_compat_base() for >> 32-bit mmap()"). >> >> The code afterwards relies on in_compat_syscall() returning true for >> 32-bit syscalls. It's usually so while we're in context of >application >> that does 32-bit syscalls. But during exec() it is not valid for x32 >ELF. >> The reason is that the application hasn't yet done any syscall, so >x32 >> bit has not being set. >> That results in -ENOMEM for x32 ELF files as there fired BAD_ADDR() >> in elf_map(), that is called from do_execve()->load_elf_binary(). >> For i386 ELFs it works as SET_PERSONALITY() sets TS_COMPAT flag. >> >> Set x32 bit before first return to userspace, during setting >personality >> at exec(). This way we can rely on in_compat_syscall() during exec(). >> Do also the reverse: drop x32 syscall bit at SET_PERSONALITY for >64-bits. >> >> Fixes: commit 1b028f784e8c ("x86/mm: Introduce mmap_compat_base() for >> 32-bit mmap()") > >Tested: >with bash:x32, mksh:amd64, posh:i386, zsh:armhf (binfmt:qemu), >fork+exec >works for every parent-child combination. > >Contrary to my naive initial reading of your fix, mixing syscalls from >a >process of the wrong ABI also works as it did before. While using a >glibc >wrapper will call the right version, x32 processes calling amd64 >syscalls is >surprisingly common -- this brings seccomp joy. > >I've attached a freestanding test case for write() and mmap(); it's >freestanding asm as most of you don't have an x32 toolchain at hand, >sorry >for unfriendly error messages. > >So with these two patches: >x86/tls: Forcibly set the accessed bit in TLS segments >x86/mm: set x32 syscall bit in SET_PERSONALITY() >everything appears to be fine. What userspace is that? Is this syscall(3) (ab)users or incorrectly ported to x32 software? -- Sent from my Android device with K-9 Mail. Please excuse my brevity. -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@xxxxxxxxx. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: <a href