linux-kernel - [PATCH v2 2/6] riscv: ftrace: align patchable functions to 4 Byte boundary

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-Id: <20240628-dev-andyc-dyn-ftrace-v4-v2-2-1e5f4cb1f049@sifive.com>
Date: Fri, 28 Jun 2024 19:47:45 +0800
From: Andy Chiu <andy.chiu@...ive.com>
To: Paul Walmsley <paul.walmsley@...ive.com>, 
 Palmer Dabbelt <palmer@...belt.com>, Albert Ou <aou@...s.berkeley.edu>, 
 Alexandre Ghiti <alexghiti@...osinc.com>, Zong Li <zong.li@...ive.com>, 
 Steven Rostedt <rostedt@...dmis.org>, 
 Masami Hiramatsu <mhiramat@...nel.org>, Mark Rutland <mark.rutland@....com>, 
 Nathan Chancellor <nathan@...nel.org>, 
 Nick Desaulniers <ndesaulniers@...gle.com>, 
 Bill Wendling <morbo@...gle.com>, Justin Stitt <justinstitt@...gle.com>, 
 Puranjay Mohan <puranjay@...nel.org>
Cc: Palmer Dabbelt <palmer@...osinc.com>, linux-riscv@...ts.infradead.org, 
 linux-kernel@...r.kernel.org, linux-trace-kernel@...r.kernel.org, 
 llvm@...ts.linux.dev, Evgenii Shatokhin <e.shatokhin@...ro.com>, 
 Andy Chiu <andy.chiu@...ive.com>
Subject: [PATCH v2 2/6] riscv: ftrace: align patchable functions to 4 Byte
 boundary

We are changing ftrace code patching in order to remove dependency from
stop_machine() and enable kernel preemption. This requires us to align
functions entry at a 4-B align address.

However, -falign-functions on older versions of GCC alone was not strong
enoungh to align all functions. In fact, cold functions are not aligned
after turning on optimizations. We consider this is a bug in GCC and
turn off guess-branch-probility as a workaround to align all functions.

GCC bug id: https://gcc.gnu.org/bugzilla/show_bug.cgi?id=88345

The option -fmin-function-alignment is able to align all functions
properly on newer versions of gcc. So, we add a cc-option to test if
the toolchain supports it.

Suggested-by: Evgenii Shatokhin <e.shatokhin@...ro.com>
Signed-off-by: Andy Chiu <andy.chiu@...ive.com>

---
Changelog v2:
 - Use CC_HAS_MIN_FUNCTION_ALIGNMENT and it friends to prevent reinventing
    wheels (Nathan)
---
 arch/riscv/Kconfig | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/arch/riscv/Kconfig b/arch/riscv/Kconfig
index 704d4683bcfa..55c70efbad0a 100644
--- a/arch/riscv/Kconfig
+++ b/arch/riscv/Kconfig
@@ -133,6 +133,7 @@ config RISCV
 	select HAVE_DEBUG_KMEMLEAK
 	select HAVE_DMA_CONTIGUOUS if MMU
 	select HAVE_DYNAMIC_FTRACE if !XIP_KERNEL && MMU && (CLANG_SUPPORTS_DYNAMIC_FTRACE || GCC_SUPPORTS_DYNAMIC_FTRACE)
+	select FUNCTION_ALIGNMENT_4B if HAVE_DYNAMIC_FTRACE && RISCV_ISA_C
 	select HAVE_DYNAMIC_FTRACE_WITH_DIRECT_CALLS
 	select HAVE_DYNAMIC_FTRACE_WITH_ARGS if HAVE_DYNAMIC_FTRACE
 	select HAVE_FTRACE_MCOUNT_RECORD if !XIP_KERNEL
@@ -208,6 +209,7 @@ config CLANG_SUPPORTS_DYNAMIC_FTRACE
 config GCC_SUPPORTS_DYNAMIC_FTRACE
 	def_bool CC_IS_GCC
 	depends on $(cc-option,-fpatchable-function-entry=8)
+	depends on CC_HAS_MIN_FUNCTION_ALIGNMENT || !RISCV_ISA_C
 
 config HAVE_SHADOW_CALL_STACK
 	def_bool $(cc-option,-fsanitize=shadow-call-stack)

-- 
2.43.0