From 78066055b08096ed3282c027de9d9e137f9a1580 Mon Sep 17 00:00:00 2001 From: Kees Cook Date: Thu, 26 Mar 2020 23:48:18 -0700 Subject: 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: Kees Cook Signed-off-by: Borislav Petkov Reviewed-by: Jason Gunthorpe Reviewed-by: Catalin Marinas Link: https://lkml.kernel.org/r/20200327064820.12602-5-keescook@chromium.org --- arch/arm/kernel/elf.c | 24 +++++++++++++++++++++--- arch/arm64/include/asm/elf.h | 20 ++++++++++++++++++++ 2 files changed, 41 insertions(+), 3 deletions(-) diff --git a/arch/arm/kernel/elf.c b/arch/arm/kernel/elf.c index 182422981386..5ccd4aced6cc 100644 --- a/arch/arm/kernel/elf.c +++ b/arch/arm/kernel/elf.c @@ -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) { diff --git a/arch/arm64/include/asm/elf.h b/arch/arm64/include/asm/elf.h index b618017205a3..986ecf41fc0f 100644 --- a/arch/arm64/include/asm/elf.h +++ b/arch/arm64/include/asm/elf.h @@ -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 -- cgit