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Message-Id: <20220203193853.21511-1-mathieu.desnoyers@efficios.com>
Date: Thu, 3 Feb 2022 14:38:51 -0500
From: Mathieu Desnoyers <mathieu.desnoyers@...icios.com>
To: Peter Zijlstra <peterz@...radead.org>
Cc: linux-kernel@...r.kernel.org,
Thomas Gleixner <tglx@...utronix.de>,
"Paul E . McKenney" <paulmck@...nel.org>,
Boqun Feng <boqun.feng@...il.com>,
"H . Peter Anvin" <hpa@...or.com>,
Paul Turner <pjt@...gle.com>,
linux-api@...r.kernel.org,
Christian Brauner <christian.brauner@...ntu.com>,
Florian Weimer <fw@...eb.enyo.de>,
David.Laight@...LAB.COM,
carlos@...hat.com,
Peter Oskolkov <posk@...k.io>,
libc-coord@...ts.openwall.com,
Mathieu Desnoyers <mathieu.desnoyers@...icios.com>
Subject: [RFC PATCH 1/3] rseq: Introduce feature size and alignment ELF auxiliary vector entries
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@...icios.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 605017eb9349..77776582e76d 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>
@@ -286,6 +287,10 @@ 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 */
diff --git a/include/uapi/linux/rseq.h b/include/uapi/linux/rseq.h
index 77ee207623a9..05d3c4cdeb40 100644
--- a/include/uapi/linux/rseq.h
+++ b/include/uapi/linux/rseq.h
@@ -130,6 +130,11 @@ struct rseq {
* this thread.
*/
__u32 flags;
+
+ /*
+ * Flexible array member at end of structure, after last feature field.
+ */
+ char end[];
} __attribute__((aligned(4 * sizeof(__u64))));
#endif /* _UAPI_LINUX_RSEQ_H */
--
2.17.1
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