Donate to e Foundation | Murena handsets with /e/OS | Own a part of Murena! Learn more

Commit 04e4f2b1 authored by Mike Frysinger's avatar Mike Frysinger Committed by Linus Torvalds
Browse files

FDPIC: Respect PT_GNU_STACK exec protection markings when creating NOMMU stack 



The current code will load the stack size and protection markings, but
then only use the markings in the MMU code path.  The NOMMU code path
always passes PROT_EXEC to the mmap() call.  While this doesn't matter
to most people whilst the code is running, it will cause a pointless
icache flush when starting every FDPIC application.  Typically this
icache flush will be of a region on the order of 128KB in size, or may
be the entire icache, depending on the facilities available on the CPU.

In the case where the arch default behaviour seems to be desired
(EXSTACK_DEFAULT), we probe VM_STACK_FLAGS for VM_EXEC to determine
whether we should be setting PROT_EXEC or not.

For arches that support an MPU (Memory Protection Unit - an MMU without
the virtual mapping capability), setting PROT_EXEC or not will make an
important difference.

It should be noted that this change also affects the executability of
the brk region, since ELF-FDPIC has that share with the stack.  However,
this is probably irrelevant as NOMMU programs aren't likely to use the
brk region, preferring instead allocation via mmap().

Signed-off-by: default avatarMike Frysinger <vapier@gentoo.org>
Signed-off-by: default avatarDavid Howells <dhowells@redhat.com>
Signed-off-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
parent 93939f4e

arch/blackfin/include/asm/page.h

+5 −0
Original line number Diff line number Diff line
@@ -10,4 +10,9 @@ 
#include <asm-generic/page.h>

#define MAP_NR(addr) (((unsigned long)(addr)-PAGE_OFFSET) >> PAGE_SHIFT)



#define VM_DATA_DEFAULT_FLAGS \

	(VM_READ | VM_WRITE | \

	((current->personality & READ_IMPLIES_EXEC) ? VM_EXEC : 0 ) | \

		 VM_MAYREAD | VM_MAYWRITE | VM_MAYEXEC)



#endif

arch/frv/include/asm/page.h

+0 −2
Original line number Diff line number Diff line
@@ -63,12 +63,10 @@ extern unsigned long max_pfn; 
#define virt_addr_valid(kaddr)	pfn_valid(__pa(kaddr) >> PAGE_SHIFT)





#ifdef CONFIG_MMU

#define VM_DATA_DEFAULT_FLAGS \

	(VM_READ | VM_WRITE | \

	((current->personality & READ_IMPLIES_EXEC) ? VM_EXEC : 0 ) | \

		 VM_MAYREAD | VM_MAYWRITE | VM_MAYEXEC)

#endif



#endif /* __ASSEMBLY__ */

fs/binfmt_elf_fdpic.c

+11 −2
Original line number Diff line number Diff line
@@ -170,6 +170,9 @@ static int load_elf_fdpic_binary(struct linux_binprm *bprm, 
	unsigned long stack_size, entryaddr;

#ifdef ELF_FDPIC_PLAT_INIT

	unsigned long dynaddr;

#endif

#ifndef CONFIG_MMU

	unsigned long stack_prot;

#endif

	struct file *interpreter = NULL; /* to shut gcc up */

	char *interpreter_name = NULL;
@@ -316,6 +319,8 @@ static int load_elf_fdpic_binary(struct linux_binprm *bprm, 
	 * defunct, deceased, etc. after this point we have to exit via

	 * error_kill */

	set_personality(PER_LINUX_FDPIC);

	if (elf_read_implies_exec(&exec_params.hdr, executable_stack))

		current->personality |= READ_IMPLIES_EXEC;

	set_binfmt(&elf_fdpic_format);



	current->mm->start_code = 0;
@@ -377,9 +382,13 @@ static int load_elf_fdpic_binary(struct linux_binprm *bprm, 
	if (stack_size < PAGE_SIZE * 2)

		stack_size = PAGE_SIZE * 2;



	stack_prot = PROT_READ | PROT_WRITE;

	if (executable_stack == EXSTACK_ENABLE_X ||

	    (executable_stack == EXSTACK_DEFAULT && VM_STACK_FLAGS & VM_EXEC))

		stack_prot |= PROT_EXEC;



	down_write(&current->mm->mmap_sem);

	current->mm->start_brk = do_mmap(NULL, 0, stack_size,

					 PROT_READ | PROT_WRITE | PROT_EXEC,

	current->mm->start_brk = do_mmap(NULL, 0, stack_size, stack_prot,

					 MAP_PRIVATE | MAP_ANONYMOUS |

					 MAP_UNINITIALIZED | MAP_GROWSDOWN,

					 0);