Messages in this thread | | | Date | Mon, 17 Oct 2022 12:09:03 -0400 | Subject | Re: [PATCH v4 01/25] rseq: Introduce feature size and alignment ELF auxiliary vector entries | From | Mathieu Desnoyers <> |
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On 2022-10-10 08:42, Florian Weimer wrote: > * 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@efficios.com> >> --- >> 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.)
I cannot imagine a use-case that would require us to bump the alignment requirement over 32 bytes, so we may very well leave it at 32. But perhaps someone else has a better imagination than mine ?
Thanks,
Mathieu
> > Thanks, > Florian >
-- Mathieu Desnoyers EfficiOS Inc. https://www.efficios.com
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