Re: [RFC PATCH 5/5] mm: introduce MADV_DOEXEC

Kirill Tkhai
2020-07-28T13:22:40Z

On 27.07.2020 20:11, Anthony Yznaga wrote:
> madvise MADV_DOEXEC preserves a memory range across exec. Initially
> only supported for non-executable, non-stack, anonymous memory.
> MADV_DONTEXEC reverts the effect of a previous MADV_DOXEXEC call and
> undoes the preservation of the range. After a successful exec call,
> the behavior of all ranges reverts to MADV_DONTEXEC.
>
> Signed-off-by: Steve Sistare <steven.sistare@oracle.com>
> Signed-off-by: Anthony Yznaga <anthony.yznaga@oracle.com>
> ---
> include/uapi/asm-generic/mman-common.h | 3 +++
> mm/madvise.c | 25 +++++++++++++++++++++++++
> 2 files changed, 28 insertions(+)
>
> diff --git a/include/uapi/asm-generic/mman-common.h b/include/uapi/asm-generic/mman-common.h
> index f94f65d429be..7c5f616b28f7 100644
> --- a/include/uapi/asm-generic/mman-common.h
> +++ b/include/uapi/asm-generic/mman-common.h
> @@ -72,6 +72,9 @@
> #define MADV_COLD 20 /* deactivate these pages */
> #define MADV_PAGEOUT 21 /* reclaim these pages */
>
> +#define MADV_DOEXEC 22 /* do inherit across exec */
> +#define MADV_DONTEXEC 23 /* don't inherit across exec */
> +
> /* compatibility flags */
> #define MAP_FILE 0
>
> diff --git a/mm/madvise.c b/mm/madvise.c
> index dd1d43cf026d..b447fa748649 100644
> --- a/mm/madvise.c
> +++ b/mm/madvise.c
> @@ -103,6 +103,26 @@ static long madvise_behavior(struct vm_area_struct *vma,
> case MADV_KEEPONFORK:
> new_flags &= ~VM_WIPEONFORK;
> break;
> + case MADV_DOEXEC:

For me MADV_KEEPONEXEC sounds better as it's symmetric to MADV_KEEPONFORK.

> + /*
> + * MADV_DOEXEC is only supported on private, non-executable,
> + * non-stack anonymous memory and if the VM_EXEC_KEEP flag
> + * is available.
> + */
> + if (!VM_EXEC_KEEP || vma->vm_file || vma->vm_flags & (VM_EXEC|VM_SHARED|VM_STACK)) {
> + error = -EINVAL;
> + goto out;
> + }
> + new_flags |= (new_flags & ~VM_MAYEXEC) | VM_EXEC_KEEP;
> + break;
> + case MADV_DONTEXEC:
> + if (!VM_EXEC_KEEP) {
> + error = -EINVAL;
> + goto out;
> + }
> + if (new_flags & VM_EXEC_KEEP)
> + new_flags |= (new_flags & ~VM_EXEC_KEEP) | VM_MAYEXEC;
> + break;
> case MADV_DONTDUMP:
> new_flags |= VM_DONTDUMP;
> break;
> @@ -983,6 +1003,8 @@ static int madvise_inject_error(int behavior,
> case MADV_SOFT_OFFLINE:
> case MADV_HWPOISON:
> #endif
> + case MADV_DOEXEC:
> + case MADV_DONTEXEC:
> return true;
>
> default:
> @@ -1037,6 +1059,9 @@ static int madvise_inject_error(int behavior,
> * MADV_DONTDUMP - the application wants to prevent pages in the given range
> * from being included in its core dump.
> * MADV_DODUMP - cancel MADV_DONTDUMP: no longer exclude from core dump.
> + * MADV_DOEXEC - On exec, preserve and duplicate this area in the new process
> + * if the new process allows it.
> + * MADV_DONTEXEC - Undo the effect of MADV_DOEXEC.
> *
> * return values:
> * zero - success
>