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Date: Wed, 3 Oct 2012 12:44:37 -0700 (PDT)
From: Hugh Dickins <hughd@...gle.com>
To: Ard Biesheuvel <ard.biesheuvel@...il.com>
cc: Andrew Morton <akpm@...ux-foundation.org>,
Kees Cook <keescook@...omium.org>, linux-kernel@...r.kernel.org
Subject: Re: Updated: [PATCH] hardening: add PROT_FINAL prot flag to
mmap/mprotect
On Wed, 3 Oct 2012, Ard Biesheuvel wrote:
> This patch adds support for the PROT_FINAL flag to
> the mmap() and mprotect() syscalls.
>
> The PROT_FINAL flag indicates that the requested set
> of protection bits should be final, i.e., it shall
> not be allowed for a subsequent mprotect call to
> set protection bits that were not set already.
>
> This is mainly intended for the dynamic linker,
> which sets up the address space on behalf of
> dynamic binaries. By using this flag, it can
> prevent exploited code from remapping read-only
> executable code or data sections read-write.
>
> Signed-off-by: Ard Biesheuvel <ard.biesheuvel@...il.com>
Acked-by: Hugh Dickins <hughd@...gle.com>
(and I rather enjoy the way you ask PROT_GROWSDOWN for an alibi, in case
someone accuses the PROT_FINAL comment of a checkpatch linelength crime.)
> ---
> arch/alpha/include/asm/mman.h | 1 +
> arch/mips/include/asm/mman.h | 1 +
> arch/parisc/include/asm/mman.h | 1 +
> arch/powerpc/include/asm/mman.h | 3 ++-
> arch/xtensa/include/asm/mman.h | 1 +
> include/asm-generic/mman-common.h | 1 +
> include/linux/mman.h | 3 ++-
> mm/mmap.c | 8 ++++++++
> mm/mprotect.c | 8 ++++++++
> 9 files changed, 25 insertions(+), 2 deletions(-)
>
> diff --git a/arch/alpha/include/asm/mman.h b/arch/alpha/include/asm/mman.h
> index cbeb361..ab46252 100644
> --- a/arch/alpha/include/asm/mman.h
> +++ b/arch/alpha/include/asm/mman.h
> @@ -6,6 +6,7 @@
> #define PROT_EXEC 0x4 /* page can be executed */
> #define PROT_SEM 0x8 /* page may be used for atomic ops */
> #define PROT_NONE 0x0 /* page can not be accessed */
> +#define PROT_FINAL 0x80 /* unset page prot bits cannot be set later */
> #define PROT_GROWSDOWN 0x01000000 /* mprotect flag: extend change to start of growsdown vma */
> #define PROT_GROWSUP 0x02000000 /* mprotect flag: extend change to end of growsup vma */
>
> diff --git a/arch/mips/include/asm/mman.h b/arch/mips/include/asm/mman.h
> index 46d3da0..9cd50e4 100644
> --- a/arch/mips/include/asm/mman.h
> +++ b/arch/mips/include/asm/mman.h
> @@ -20,6 +20,7 @@
> #define PROT_EXEC 0x04 /* page can be executed */
> /* 0x08 reserved for PROT_EXEC_NOFLUSH */
> #define PROT_SEM 0x10 /* page may be used for atomic ops */
> +#define PROT_FINAL 0x80 /* unset page prot bits cannot be set later */
> #define PROT_GROWSDOWN 0x01000000 /* mprotect flag: extend change to start of growsdown vma */
> #define PROT_GROWSUP 0x02000000 /* mprotect flag: extend change to end of growsup vma */
>
> diff --git a/arch/parisc/include/asm/mman.h b/arch/parisc/include/asm/mman.h
> index 12219eb..0cf18e3 100644
> --- a/arch/parisc/include/asm/mman.h
> +++ b/arch/parisc/include/asm/mman.h
> @@ -6,6 +6,7 @@
> #define PROT_EXEC 0x4 /* page can be executed */
> #define PROT_SEM 0x8 /* page may be used for atomic ops */
> #define PROT_NONE 0x0 /* page can not be accessed */
> +#define PROT_FINAL 0x80 /* unset page prot bits cannot be set later */
> #define PROT_GROWSDOWN 0x01000000 /* mprotect flag: extend change to start of growsdown vma */
> #define PROT_GROWSUP 0x02000000 /* mprotect flag: extend change to end of growsup vma */
>
> diff --git a/arch/powerpc/include/asm/mman.h b/arch/powerpc/include/asm/mman.h
> index d4a7f64..c0014eb 100644
> --- a/arch/powerpc/include/asm/mman.h
> +++ b/arch/powerpc/include/asm/mman.h
> @@ -52,7 +52,8 @@ static inline pgprot_t arch_vm_get_page_prot(unsigned long vm_flags)
>
> static inline int arch_validate_prot(unsigned long prot)
> {
> - if (prot & ~(PROT_READ | PROT_WRITE | PROT_EXEC | PROT_SEM | PROT_SAO))
> + if (prot & ~(PROT_READ | PROT_WRITE | PROT_EXEC | PROT_SEM
> + | PROT_SAO | PROT_FINAL))
> return 0;
> if ((prot & PROT_SAO) && !cpu_has_feature(CPU_FTR_SAO))
> return 0;
> diff --git a/arch/xtensa/include/asm/mman.h b/arch/xtensa/include/asm/mman.h
> index 25bc6c1..680b3c4 100644
> --- a/arch/xtensa/include/asm/mman.h
> +++ b/arch/xtensa/include/asm/mman.h
> @@ -27,6 +27,7 @@
> #define PROT_EXEC 0x4 /* page can be executed */
>
> #define PROT_SEM 0x10 /* page may be used for atomic ops */
> +#define PROT_FINAL 0x80 /* unset page prot bits cannot be set later */
> #define PROT_GROWSDOWN 0x01000000 /* mprotect flag: extend change to start of growsdown vma */
> #define PROT_GROWSUP 0x02000000 /* mprotect flag: extend change to end fo growsup vma */
>
> diff --git a/include/asm-generic/mman-common.h b/include/asm-generic/mman-common.h
> index d030d2c..5687993 100644
> --- a/include/asm-generic/mman-common.h
> +++ b/include/asm-generic/mman-common.h
> @@ -10,6 +10,7 @@
> #define PROT_WRITE 0x2 /* page can be written */
> #define PROT_EXEC 0x4 /* page can be executed */
> #define PROT_SEM 0x8 /* page may be used for atomic ops */
> +#define PROT_FINAL 0x80 /* unset page prot bits cannot be set later */
> #define PROT_NONE 0x0 /* page can not be accessed */
> #define PROT_GROWSDOWN 0x01000000 /* mprotect flag: extend change to start of growsdown vma */
> #define PROT_GROWSUP 0x02000000 /* mprotect flag: extend change to end of growsup vma */
> diff --git a/include/linux/mman.h b/include/linux/mman.h
> index 8b74e9b..c11b1ab 100644
> --- a/include/linux/mman.h
> +++ b/include/linux/mman.h
> @@ -51,7 +51,8 @@ static inline void vm_unacct_memory(long pages)
> */
> static inline int arch_validate_prot(unsigned long prot)
> {
> - return (prot & ~(PROT_READ | PROT_WRITE | PROT_EXEC | PROT_SEM)) == 0;
> + return (prot & ~(PROT_READ | PROT_WRITE | PROT_EXEC
> + | PROT_SEM | PROT_FINAL)) == 0;
> }
> #define arch_validate_prot arch_validate_prot
> #endif
> diff --git a/mm/mmap.c b/mm/mmap.c
> index 872441e..292f988 100644
> --- a/mm/mmap.c
> +++ b/mm/mmap.c
> @@ -1101,6 +1101,14 @@ unsigned long do_mmap_pgoff(struct file *file, unsigned long addr,
> }
> }
>
> + /*
> + * PROT_FINAL indicates that prot bits not requested by this
> + * mmap() call cannot be added later
> + */
> + if (prot & PROT_FINAL)
> + vm_flags &= ~(VM_MAYREAD | VM_MAYWRITE | VM_MAYEXEC)
> + | (vm_flags << 4);
> +
> return mmap_region(file, addr, len, flags, vm_flags, pgoff);
> }
>
> diff --git a/mm/mprotect.c b/mm/mprotect.c
> index a409926..7a39f73 100644
> --- a/mm/mprotect.c
> +++ b/mm/mprotect.c
> @@ -301,6 +301,14 @@ SYSCALL_DEFINE3(mprotect, unsigned long, start, size_t, len,
> goto out;
> }
>
> + /*
> + * PROT_FINAL indicates that prot bits removed by this
> + * mprotect() call cannot be added later
> + */
> + if (prot & PROT_FINAL)
> + newflags &= ~(VM_MAYREAD | VM_MAYWRITE | VM_MAYEXEC)
> + | (newflags << 4);
> +
> error = security_file_mprotect(vma, reqprot, prot);
> if (error)
> goto out;
> --
> 1.7.9.5
>
>
>
--
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