Add a table to document the current behavior of READ_IMPLIES_EXEC in preparation for changing the behavior. Signed-off-by: Kees Cook <keescook@xxxxxxxxxxxx> Reviewed-by: Jason Gunthorpe <jgg@xxxxxxxxxxxx> --- arch/x86/include/asm/elf.h | 19 +++++++++++++++++++ 1 file changed, 19 insertions(+) diff --git a/arch/x86/include/asm/elf.h b/arch/x86/include/asm/elf.h index 69c0f892e310..ee459d4c3b45 100644 --- a/arch/x86/include/asm/elf.h +++ b/arch/x86/include/asm/elf.h @@ -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@xxxxxxxxxxxx + * */ #define elf_read_implies_exec(ex, executable_stack) \ (executable_stack != EXSTACK_DISABLE_X) -- 2.20.1
