From: Ard Biesheuvel <ardb+git@google.com>
To: linux-arm-kernel@lists.infradead.org
Cc: will@kernel.org, catalin.marinas@arm.com, mark.rutland@arm.com,
Ard Biesheuvel <ardb@kernel.org>,
Sami Tolvanen <samitolvanen@google.com>,
Kees Cook <keescook@chromium.org>
Subject: [PATCH 2/2] arm64: scs: Disable LTO for SCS patching code
Date: Tue, 23 Jan 2024 14:30:55 +0100 [thread overview]
Message-ID: <20240123133052.1417449-6-ardb+git@google.com> (raw)
In-Reply-To: <20240123133052.1417449-4-ardb+git@google.com>
From: Ard Biesheuvel <ardb@kernel.org>
Full LTO takes the '-mbranch-protection=none' passed to the compiler
when generating the dynamic shadow call stack patching code as a hint to
stop emitting PAC instructions altogether. (Thin LTO appears unaffected
by this)
Work around this by disabling LTO for the compilation unit, which
appears to convince the linker that it should still use PAC in the rest
of the kernel..
Fixes: 3b619e22c460 ("arm64: implement dynamic shadow call stack for Clang")
Signed-off-by: Ard Biesheuvel <ardb@kernel.org>
---
arch/arm64/kernel/Makefile | 6 ++++++
1 file changed, 6 insertions(+)
diff --git a/arch/arm64/kernel/Makefile b/arch/arm64/kernel/Makefile
index d95b3d6b471a..467cb7117273 100644
--- a/arch/arm64/kernel/Makefile
+++ b/arch/arm64/kernel/Makefile
@@ -73,7 +73,13 @@ obj-$(CONFIG_ARM64_MTE) += mte.o
obj-y += vdso-wrap.o
obj-$(CONFIG_COMPAT_VDSO) += vdso32-wrap.o
obj-$(CONFIG_UNWIND_PATCH_PAC_INTO_SCS) += patch-scs.o
+
+# We need to prevent the SCS patching code from patching itself. Using
+# -mbranch-protection=none here to avoid the patchable PAC opcodes from being
+# generated triggers an issue with full LTO on Clang, which stops emitting PAC
+# instructions altogether. So disable LTO as well for the compilation unit.
CFLAGS_patch-scs.o += -mbranch-protection=none
+CFLAGS_REMOVE_patch-scs.o += $(CC_FLAGS_LTO)
# Force dependency (vdso*-wrap.S includes vdso.so through incbin)
$(obj)/vdso-wrap.o: $(obj)/vdso/vdso.so
--
2.43.0.429.g432eaa2c6b-goog
_______________________________________________
linux-arm-kernel mailing list
linux-arm-kernel@lists.infradead.org
http://lists.infradead.org/mailman/listinfo/linux-arm-kernel
next prev parent reply other threads:[~2024-01-23 13:31 UTC|newest]
Thread overview: 6+ messages / expand[flat|nested] mbox.gz Atom feed top
2024-01-23 13:30 [PATCH 0/2] arm64: Fix for dynamic SCS under full LTO take #2 Ard Biesheuvel
2024-01-23 13:30 ` [PATCH 1/2] arm64: Revert "scs: Work around full LTO issue with dynamic SCS" Ard Biesheuvel
2024-01-23 13:30 ` Ard Biesheuvel [this message]
2024-01-23 17:06 ` [PATCH 0/2] arm64: Fix for dynamic SCS under full LTO take #2 Sami Tolvanen
2024-01-23 22:27 ` Kees Cook
2024-01-30 13:14 ` Will Deacon
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=20240123133052.1417449-6-ardb+git@google.com \
--to=ardb+git@google.com \
--cc=ardb@kernel.org \
--cc=catalin.marinas@arm.com \
--cc=keescook@chromium.org \
--cc=linux-arm-kernel@lists.infradead.org \
--cc=mark.rutland@arm.com \
--cc=samitolvanen@google.com \
--cc=will@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).