Commit 9d9e435f authored by Kees Cook's avatar Kees Cook Committed by Borislav Petkov
Browse files

x86/elf: Add table to document READ_IMPLIES_EXEC 



Add a table to document the current behavior of READ_IMPLIES_EXEC in
preparation for changing the behavior.

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/20200327064820.12602-2-keescook@chromium.org
parent ae83d0b4

arch/x86/include/asm/elf.h

+19 −0
Original line number Diff line number Diff line
@@ -281,6 +281,25 @@ extern u32 elf_hwcap2; 
/*

 * An executable for which elf_read_implies_exec() returns TRUE will

 * have the READ_IMPLIES_EXEC personality flag set automatically.

 *

 * The decision process for determining the results are:

 *

 *                 CPU: | lacks NX*  | has NX, ia32     | has NX, x86_64 |

 * ELF:                 |            |                  |                |

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

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

 * PT_GNU_STACK == RWX  | exec-all   | exec-all         | exec-all       |

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

 *

 *  exec-all  : all PROT_READ user mappings are executable, except when

 *              backed by files on a noexec-filesystem.

 *  exec-none : only PROT_EXEC user mappings are executable.

 *

 *  *this column has no architectural effect: NX markings are ignored by

 *   hardware, but may have behavioral effects when "wants X" collides with

 *   "cannot be X" constraints in memory permission flags, as in

 *   https://lkml.kernel.org/r/20190418055759.GA3155@mellanox.com

 *

 */

#define elf_read_implies_exec(ex, executable_stack)	\

	(executable_stack != EXSTACK_DISABLE_X)