Commit 9fccc5c0 authored by Kees Cook's avatar Kees Cook Committed by Borislav Petkov
Browse files

x86/elf: Disable automatic READ_IMPLIES_EXEC on 64-bit 



With modern x86 64-bit environments, there should never be a need for
automatic READ_IMPLIES_EXEC, as the architecture is intended to always
be execute-bit aware (as in, the default memory protection should be NX
unless a region explicitly requests to be executable).

There were very old x86_64 systems that lacked the NX bit, but for those,
the NX bit is, obviously, unenforceable, so these changes should have
no impact on them.

Suggested-by: default avatarHector Marco-Gisbert <hecmargi@upv.es>
Signed-off-by: default avatarKees Cook <keescook@chromium.org>
Signed-off-by: default avatarBorislav Petkov <bp@suse.de>
Reviewed-by: default avatarJason Gunthorpe <jgg@mellanox.com>
Link: https://lkml.kernel.org/r/20200327064820.12602-4-keescook@chromium.org
parent 12230611

arch/x86/include/asm/elf.h

+2 −2
Original line number Diff line number Diff line
@@ -287,7 +287,7 @@ extern u32 elf_hwcap2; 
 *                 CPU: | lacks NX*  | has NX, ia32     | has NX, x86_64 |

 * ELF:                 |            |                  |                |

 * ---------------------|------------|------------------|----------------|

 * missing PT_GNU_STACK | exec-all   | exec-all         | exec-all       |

 * missing PT_GNU_STACK | exec-all   | exec-all         | exec-none      |

 * PT_GNU_STACK == RWX  | exec-stack | exec-stack       | exec-stack     |

 * PT_GNU_STACK == RW   | exec-none  | exec-none        | exec-none      |

 *
@@ -303,7 +303,7 @@ extern u32 elf_hwcap2; 
 *

 */

#define elf_read_implies_exec(ex, executable_stack)	\

	(executable_stack == EXSTACK_DEFAULT)

	(mmap_is_ia32() && executable_stack == EXSTACK_DEFAULT)



struct task_struct;