* Mathieu Desnoyers:
> Export the rseq feature size supported by the kernel as well as the
> required allocation alignment for the rseq per-thread area to user-space
> through ELF auxiliary vector entries.
>
> This is part of the extensible rseq ABI.
>
> Signed-off-by: Mathieu Desnoyers <mathieu.desnoyers@xxxxxxxxxxxx>
> ---
> fs/binfmt_elf.c | 5 +++++
> include/uapi/linux/auxvec.h | 2 ++
> include/uapi/linux/rseq.h | 5 +++++
> 3 files changed, 12 insertions(+)
>
> diff --git a/fs/binfmt_elf.c b/fs/binfmt_elf.c
> index 63c7ebb0da89..04fca1e4cbd2 100644
> --- a/fs/binfmt_elf.c
> +++ b/fs/binfmt_elf.c
> @@ -46,6 +46,7 @@
> #include <linux/cred.h>
> #include <linux/dax.h>
> #include <linux/uaccess.h>
> +#include <linux/rseq.h>
> #include <asm/param.h>
> #include <asm/page.h>
>
> @@ -288,6 +289,10 @@ create_elf_tables(struct linux_binprm *bprm, const struct elfhdr *exec,
> if (bprm->have_execfd) {
> NEW_AUX_ENT(AT_EXECFD, bprm->execfd);
> }
> +#ifdef CONFIG_RSEQ
> + NEW_AUX_ENT(AT_RSEQ_FEATURE_SIZE, offsetof(struct rseq, end));
> + NEW_AUX_ENT(AT_RSEQ_ALIGN, __alignof__(struct rseq));
> +#endif
> #undef NEW_AUX_ENT
> /* AT_NULL is zero; clear the rest too */
> memset(elf_info, 0, (char *)mm->saved_auxv +
> diff --git a/include/uapi/linux/auxvec.h b/include/uapi/linux/auxvec.h
> index c7e502bf5a6f..6991c4b8ab18 100644
> --- a/include/uapi/linux/auxvec.h
> +++ b/include/uapi/linux/auxvec.h
> @@ -30,6 +30,8 @@
> * differ from AT_PLATFORM. */
> #define AT_RANDOM 25 /* address of 16 random bytes */
> #define AT_HWCAP2 26 /* extension of AT_HWCAP */
> +#define AT_RSEQ_FEATURE_SIZE 27 /* rseq supported feature size */
> +#define AT_RSEQ_ALIGN 28 /* rseq allocation alignment */
>
> #define AT_EXECFN 31 /* filename of program */
Do we need the alignment? Or can we keep it perpetually at 32? Or we
could steal some bits from AT_RSEQ_FEATURE_SIZE? (Not the lower
bits—they aren't unused due to the way the feature size works.)
Thanks,
Florian
