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rseq: Introduce feature size and alignment ELF auxiliary vector entries

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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>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Link: https://lore.kernel.org/r/20221122203932.231377-3-mathieu.desnoyers@efficios.com
This commit is contained in:
Mathieu Desnoyers 2022-11-22 15:39:04 -05:00 • committed by Peter Zijlstra
parent 4842dadfc6
commit 317c8194e6
3 changed files with 12 additions and 0 deletions
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5
fs/binfmt_elf.c
View file

@ -46,6 +46,7 @@
#include <linux/cred.h> #include <linux/cred.h>
#include <linux/dax.h> #include <linux/dax.h>
#include <linux/uaccess.h> #include <linux/uaccess.h>
#include <linux/rseq.h>
#include <asm/param.h> #include <asm/param.h>
#include <asm/page.h> #include <asm/page.h>
@ -288,6 +289,10 @@ create_elf_tables(struct linux_binprm *bprm, const struct elfhdr *exec,
if (bprm->have_execfd) { if (bprm->have_execfd) {
NEW_AUX_ENT(AT_EXECFD, bprm->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 #undef NEW_AUX_ENT
/* AT_NULL is zero; clear the rest too */ /* AT_NULL is zero; clear the rest too */
memset(elf_info, 0, (char *)mm->saved_auxv + memset(elf_info, 0, (char *)mm->saved_auxv +

2
include/uapi/linux/auxvec.h
View file

@ -30,6 +30,8 @@
* differ from AT_PLATFORM. */ * differ from AT_PLATFORM. */
#define AT_RANDOM 25 /* address of 16 random bytes */ #define AT_RANDOM 25 /* address of 16 random bytes */
#define AT_HWCAP2 26 /* extension of AT_HWCAP */ #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 */ #define AT_EXECFN 31 /* filename of program */

5
include/uapi/linux/rseq.h
View file

@ -130,6 +130,11 @@ struct rseq {
* this thread. * this thread.
*/ */
__u32 flags; __u32 flags;
/*
* Flexible array member at end of structure, after last feature field.
*/
char end[];
} __attribute__((aligned(4 * sizeof(__u64)))); } __attribute__((aligned(4 * sizeof(__u64))));
#endif /* _UAPI_LINUX_RSEQ_H */ #endif /* _UAPI_LINUX_RSEQ_H */