Commit 78066055 authored by Kees Cook's avatar Kees Cook Committed by Borislav Petkov
Browse files

arm32/64/elf: Add tables to document READ_IMPLIES_EXEC 



Add tables to document the current behavior of READ_IMPLIES_EXEC in
preparation for changing the behavior for both arm64 and arm.

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>
Reviewed-by: default avatarCatalin Marinas <catalin.marinas@arm.com>
Link: https://lkml.kernel.org/r/20200327064820.12602-5-keescook@chromium.org
parent 9fccc5c0

arch/arm/kernel/elf.c

+21 −3
Original line number Diff line number Diff line
@@ -78,9 +78,27 @@ void elf_set_personality(const struct elf32_hdr *x) 
EXPORT_SYMBOL(elf_set_personality);



/*

 * Set READ_IMPLIES_EXEC if:

 *  - the binary requires an executable stack

 *  - we're running on a CPU which doesn't support NX.

 * 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     |

 * ELF:                 |            |            |

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

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

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

 * PT_GNU_STACK == RW   | exec-all   | 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

 *

 */

int arm_elf_read_implies_exec(int executable_stack)

{

arch/arm64/include/asm/elf.h

+20 −0
Original line number Diff line number Diff line
@@ -96,6 +96,26 @@ 
 */

#define elf_check_arch(x)		((x)->e_machine == EM_AARCH64)



/*

 * 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*: | arm32      | arm64      |

 * ELF:                 |            |            |

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

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

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

 * PT_GNU_STACK == RW   | 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.

 *

 *  *all arm64 CPUs support NX, so there is no "lacks NX" column.

 *

 */

#define elf_read_implies_exec(ex,stk)	(stk != EXSTACK_DISABLE_X)



#define CORE_DUMP_USE_REGSET