From: "tip-bot2 for Nick Desaulniers" <tip-bot2@linutronix.de>
To: linux-tip-commits@vger.kernel.org
Cc: Nick Desaulniers <ndesaulniers@google.com>,
Kees Cook <keescook@chromium.org>,
Thomas Gleixner <tglx@linutronix.de>,
Nathan Chancellor <nathan@kernel.org>,
x86@kernel.org, linux-kernel@vger.kernel.org
Subject: [tip: core/urgent] stack: Replace "o" output with "r" input constraint
Date: Tue, 11 May 2021 08:02:35 -0000 [thread overview]
Message-ID: <162072015599.29796.13527415433369376189.tip-bot2@tip-bot2> (raw)
In-Reply-To: <20210419231741.4084415-1-keescook@chromium.org>
The following commit has been merged into the core/urgent branch of tip:
Commit-ID: 2515dd6ce8e545b0b2eece84920048ef9ed846c4
Gitweb: https://git.kernel.org/tip/2515dd6ce8e545b0b2eece84920048ef9ed846c4
Author: Nick Desaulniers <ndesaulniers@google.com>
AuthorDate: Mon, 19 Apr 2021 16:17:41 -07:00
Committer: Thomas Gleixner <tglx@linutronix.de>
CommitterDate: Tue, 11 May 2021 09:56:11 +02:00
stack: Replace "o" output with "r" input constraint
"o" isn't a common asm() constraint to use; it triggers an assertion in
assert-enabled builds of LLVM that it's not recognized when targeting
aarch64 (though it appears to fall back to "m"). It's fixed in LLVM 13 now,
but there isn't really a good reason to use "o" in particular here. To
avoid causing build issues for those using assert-enabled builds of earlier
LLVM versions, the constraint needs changing.
Instead, if the point is to retain the __builtin_alloca(), make ptr appear
to "escape" via being an input to an empty inline asm block. This is
preferable anyways, since otherwise this looks like a dead store.
While the use of "r" was considered in
https://lore.kernel.org/lkml/202104011447.2E7F543@keescook/
it was only tested as an output (which looks like a dead store, and wasn't
sufficient).
Use "r" as an input constraint instead, which behaves correctly across
compilers and architectures.
Fixes: 39218ff4c625 ("stack: Optionally randomize kernel stack offset each syscall")
Signed-off-by: Nick Desaulniers <ndesaulniers@google.com>
Signed-off-by: Kees Cook <keescook@chromium.org>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Tested-by: Kees Cook <keescook@chromium.org>
Tested-by: Nathan Chancellor <nathan@kernel.org>
Reviewed-by: Nathan Chancellor <nathan@kernel.org>
Link: https://reviews.llvm.org/D100412
Link: https://bugs.llvm.org/show_bug.cgi?id=49956
Link: https://lore.kernel.org/r/20210419231741.4084415-1-keescook@chromium.org
---
include/linux/randomize_kstack.h | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)
diff --git a/include/linux/randomize_kstack.h b/include/linux/randomize_kstack.h
index fd80fab..bebc911 100644
--- a/include/linux/randomize_kstack.h
+++ b/include/linux/randomize_kstack.h
@@ -38,7 +38,7 @@ void *__builtin_alloca(size_t size);
u32 offset = raw_cpu_read(kstack_offset); \
u8 *ptr = __builtin_alloca(KSTACK_OFFSET_MAX(offset)); \
/* Keep allocation even after "ptr" loses scope. */ \
- asm volatile("" : "=o"(*ptr) :: "memory"); \
+ asm volatile("" :: "r"(ptr) : "memory"); \
} \
} while (0)
prev parent reply other threads:[~2021-05-11 8:02 UTC|newest]
Thread overview: 5+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-04-19 23:17 [PATCH] stack: replace "o" output with "r" input constraint Kees Cook
2021-04-23 1:02 ` Nathan Chancellor
2021-05-05 21:12 ` Nathan Chancellor
2021-05-05 21:19 ` Kees Cook
2021-05-11 8:02 ` tip-bot2 for Nick Desaulniers [this message]
Reply instructions:
You may reply publicly to this message via plain-text email
using any one of the following methods:
* Save the following mbox file, import it into your mail client,
and reply-to-all from there: mbox
Avoid top-posting and favor interleaved quoting:
https://en.wikipedia.org/wiki/Posting_style#Interleaved_style
* Reply using the --to, --cc, and --in-reply-to
switches of git-send-email(1):
git send-email \
--in-reply-to=162072015599.29796.13527415433369376189.tip-bot2@tip-bot2 \
--to=tip-bot2@linutronix.de \
--cc=keescook@chromium.org \
--cc=linux-kernel@vger.kernel.org \
--cc=linux-tip-commits@vger.kernel.org \
--cc=nathan@kernel.org \
--cc=ndesaulniers@google.com \
--cc=tglx@linutronix.de \
--cc=x86@kernel.org \
/path/to/YOUR_REPLY
https://kernel.org/pub/software/scm/git/docs/git-send-email.html
* If your mail client supports setting the In-Reply-To header
via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line
before the message body.
This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for NNTP newsgroup(s).