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: Mike Frysinger <vapier@gentoo.org>
Signed-off-by: David Howells <dhowells@redhat.com>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

diff --git a/arch/blackfin/include/asm/page.h b/arch/blackfin/include/asm/page.h
index 944a07c6cfd6084500347ef3b440786d2d546bd9..1d04e4078340c5617f67ba7bbc92d6a4975dc06a 100644 (file)
--- a/arch/blackfin/include/asm/page.h
+++ b/arch/blackfin/include/asm/page.h
@@ -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

diff --git a/arch/frv/include/asm/page.h b/arch/frv/include/asm/page.h
index 25c6a5002355da190f88b90c5d8954b912453a6f..8c97068ac8fc4543cf288629cf9e85db57887431 100644 (file)
--- a/arch/frv/include/asm/page.h
+++ b/arch/frv/include/asm/page.h
@@ -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__ */
 

diff --git a/fs/binfmt_elf_fdpic.c b/fs/binfmt_elf_fdpic.c
index 7dc85997e96c36c51eb8a3319a706224031b3ebd..c57d9ce5ff7ef85605786fc26200b3fe76df93df 100644 (file)
--- a/fs/binfmt_elf_fdpic.c
+++ b/fs/binfmt_elf_fdpic.c
@@ -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);