4.16-stable review patch. If anyone has any objections, please let me know.
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From: Dmitry Safonov dima@arista.com
commit acf46020012ccbca1172e9c7aeab399c950d9212 upstream.
The x86 mmap() code selects the mmap base for an allocation depending on the bitness of the syscall. For 64bit sycalls it select mm->mmap_base and for 32bit mm->mmap_compat_base.
exec() calls mmap() which in turn uses in_compat_syscall() to check whether the mapping is for a 32bit or a 64bit task. The decision is made on the following criteria:
ia32 child->thread.status & TS_COMPAT x32 child->pt_regs.orig_ax & __X32_SYSCALL_BIT ia64 !ia32 && !x32
__set_personality_x32() was dropping TS_COMPAT flag, but set_personality_64bit() has kept compat syscall flag making in_compat_syscall() return true during the first exec() syscall.
Which in result has user-visible effects, mentioned by Alexey: 1) It breaks ASAN $ gcc -fsanitize=address wrap.c -o wrap-asan $ ./wrap32 ./wrap-asan true ==1217==Shadow memory range interleaves with an existing memory mapping. ASan cannot proceed correctly. ABORTING. ==1217==ASan shadow was supposed to be located in the [0x00007fff7000-0x10007fff7fff] range. ==1217==Process memory map follows: 0x000000400000-0x000000401000 /home/izbyshev/test/gcc/asan-exec-from-32bit/wrap-asan 0x000000600000-0x000000601000 /home/izbyshev/test/gcc/asan-exec-from-32bit/wrap-asan 0x000000601000-0x000000602000 /home/izbyshev/test/gcc/asan-exec-from-32bit/wrap-asan 0x0000f7dbd000-0x0000f7de2000 /lib64/ld-2.27.so 0x0000f7fe2000-0x0000f7fe3000 /lib64/ld-2.27.so 0x0000f7fe3000-0x0000f7fe4000 /lib64/ld-2.27.so 0x0000f7fe4000-0x0000f7fe5000 0x7fed9abff000-0x7fed9af54000 0x7fed9af54000-0x7fed9af6b000 /lib64/libgcc_s.so.1 [snip]
2) It doesn't seem to be great for security if an attacker always knows that ld.so is going to be mapped into the first 4GB in this case (the same thing happens for PIEs as well).
The testcase: $ cat wrap.c
int main(int argc, char *argv[]) { execvp(argv[1], &argv[1]); return 127; }
$ gcc wrap.c -o wrap $ LD_SHOW_AUXV=1 ./wrap ./wrap true |& grep AT_BASE AT_BASE: 0x7f63b8309000 AT_BASE: 0x7faec143c000 AT_BASE: 0x7fbdb25fa000
$ gcc -m32 wrap.c -o wrap32 $ LD_SHOW_AUXV=1 ./wrap32 ./wrap true |& grep AT_BASE AT_BASE: 0xf7eff000 AT_BASE: 0xf7cee000 AT_BASE: 0x7f8b9774e000
Fixes: 1b028f784e8c ("x86/mm: Introduce mmap_compat_base() for 32-bit mmap()") Fixes: ada26481dfe6 ("x86/mm: Make in_compat_syscall() work during exec") Reported-by: Alexey Izbyshev izbyshev@ispras.ru Bisected-by: Alexander Monakov amonakov@ispras.ru Investigated-by: Andy Lutomirski luto@kernel.org Signed-off-by: Dmitry Safonov dima@arista.com Signed-off-by: Thomas Gleixner tglx@linutronix.de Reviewed-by: Cyrill Gorcunov gorcunov@openvz.org Cc: Borislav Petkov bp@suse.de Cc: Alexander Monakov amonakov@ispras.ru Cc: Dmitry Safonov 0x7f454c46@gmail.com Cc: stable@vger.kernel.org Cc: linux-mm@kvack.org Cc: Andy Lutomirski luto@kernel.org Cc: "H. Peter Anvin" hpa@zytor.com Cc: Cyrill Gorcunov gorcunov@openvz.org Cc: "Kirill A. Shutemov" kirill.shutemov@linux.intel.com Link: https://lkml.kernel.org/r/20180517233510.24996-1-dima@arista.com Signed-off-by: Greg Kroah-Hartman gregkh@linuxfoundation.org
--- arch/x86/kernel/process_64.c | 1 + 1 file changed, 1 insertion(+)
--- a/arch/x86/kernel/process_64.c +++ b/arch/x86/kernel/process_64.c @@ -528,6 +528,7 @@ void set_personality_64bit(void) clear_thread_flag(TIF_X32); /* Pretend that this comes from a 64bit execve */ task_pt_regs(current)->orig_ax = __NR_execve; + current_thread_info()->status &= ~TS_COMPAT;
/* Ensure the corresponding mm is not marked. */ if (current->mm)