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From: Kees Cook <keescook@chromium.org>
To: Ingo Molnar <mingo@kernel.org>
Cc: "Kees Cook" <keescook@chromium.org>,
	"Nick Desaulniers" <ndesaulniers@google.com>,
	"Jian Cai" <jiancai@google.com>,
	"Fāng-ruì Sòng" <maskray@google.com>,
	"Luis Lozano" <llozano@google.com>,
	"Manoj Gupta" <manojgupta@google.com>,
	stable@vger.kernel.org,
	"Catalin Marinas" <catalin.marinas@arm.com>,
	"Mark Rutland" <mark.rutland@arm.com>,
	"Ard Biesheuvel" <ardb@kernel.org>,
	"Peter Collingbourne" <pcc@google.com>,
	"James Morse" <james.morse@arm.com>,
	"Borislav Petkov" <bp@suse.de>, "Ingo Molnar" <mingo@redhat.com>,
	"Russell King" <linux@armlinux.org.uk>,
	"Masahiro Yamada" <masahiroy@kernel.org>,
	"Arvind Sankar" <nivedita@alum.mit.edu>,
	"Nathan Chancellor" <natechancellor@gmail.com>,
	"Arnd Bergmann" <arnd@arndb.de>,
	x86@kernel.org, clang-built-linux@googlegroups.com,
	linux-arch@vger.kernel.org, linux-efi@vger.kernel.org,
	linux-arm-kernel@lists.infradead.org,
	linux-kernel@vger.kernel.org
Subject: [PATCH v6 06/29] vmlinux.lds.h: add PGO and AutoFDO input sections
Date: Fri, 21 Aug 2020 12:42:47 -0700
Message-ID: <20200821194310.3089815-7-keescook@chromium.org> (raw)
In-Reply-To: <20200821194310.3089815-1-keescook@chromium.org>

From: Nick Desaulniers <ndesaulniers@google.com>

Basically, consider .text.{hot|unlikely|unknown}.* part of .text, too.

When compiling with profiling information (collected via PGO
instrumentations or AutoFDO sampling), Clang will separate code into
.text.hot, .text.unlikely, or .text.unknown sections based on profiling
information. After D79600 (clang-11), these sections will have a
trailing `.` suffix, ie.  .text.hot., .text.unlikely., .text.unknown..

When using -ffunction-sections together with profiling infomation,
either explicitly (FGKASLR) or implicitly (LTO), code may be placed in
sections following the convention:
.text.hot.<foo>, .text.unlikely.<bar>, .text.unknown.<baz>
where <foo>, <bar>, and <baz> are functions.  (This produces one section
per function; we generally try to merge these all back via linker script
so that we don't have 50k sections).

For the above cases, we need to teach our linker scripts that such
sections might exist and that we'd explicitly like them grouped
together, otherwise we can wind up with code outside of the
_stext/_etext boundaries that might not be mapped properly for some
architectures, resulting in boot failures.

If the linker script is not told about possible input sections, then
where the section is placed as output is a heuristic-laiden mess that's
non-portable between linkers (ie. BFD and LLD), and has resulted in many
hard to debug bugs.  Kees Cook is working on cleaning this up by adding
--orphan-handling=warn linker flag used in ARCH=powerpc to additional
architectures. In the case of linker scripts, borrowing from the Zen of
Python: explicit is better than implicit.

Also, ld.bfd's internal linker script considers .text.hot AND
.text.hot.* to be part of .text, as well as .text.unlikely and
.text.unlikely.*. I didn't see support for .text.unknown.*, and didn't
see Clang producing such code in our kernel builds, but I see code in
LLVM that can produce such section names if profiling information is
missing. That may point to a larger issue with generating or collecting
profiles, but I would much rather be safe and explicit than have to
debug yet another issue related to orphan section placement.

Reported-by: Jian Cai <jiancai@google.com>
Suggested-by: Fāng-ruì Sòng <maskray@google.com>
Tested-by: Luis Lozano <llozano@google.com>
Tested-by: Manoj Gupta <manojgupta@google.com>
Acked-by: Kees Cook <keescook@chromium.org>
Cc: stable@vger.kernel.org
Link: https://sourceware.org/git/?p=binutils-gdb.git;a=commitdiff;h=add44f8d5c5c05e08b11e033127a744d61c26aee
Link: https://sourceware.org/git/?p=binutils-gdb.git;a=commitdiff;h=1de778ed23ce7492c523d5850c6c6dbb34152655
Link: https://reviews.llvm.org/D79600
Link: https://bugs.chromium.org/p/chromium/issues/detail?id=1084760
Debugged-by: Luis Lozano <llozano@google.com>
Signed-off-by: Nick Desaulniers <ndesaulniers@google.com>
Signed-off-by: Kees Cook <keescook@chromium.org>
---
 include/asm-generic/vmlinux.lds.h | 5 ++++-
 1 file changed, 4 insertions(+), 1 deletion(-)

diff --git a/include/asm-generic/vmlinux.lds.h b/include/asm-generic/vmlinux.lds.h
index 98d013dcc11a..91dcfb91ac45 100644
--- a/include/asm-generic/vmlinux.lds.h
+++ b/include/asm-generic/vmlinux.lds.h
@@ -581,7 +581,10 @@
  */
 #define TEXT_TEXT							\
 		ALIGN_FUNCTION();					\
-		*(.text.hot TEXT_MAIN .text.fixup .text.unlikely)	\
+		*(.text.hot .text.hot.*)				\
+		*(TEXT_MAIN .text.fixup)				\
+		*(.text.unlikely .text.unlikely.*)			\
+		*(.text.unknown .text.unknown.*)			\
 		NOINSTR_TEXT						\
 		*(.text..refcount)					\
 		*(.ref.text)						\
-- 
2.25.1


  parent reply index

Thread overview: 92+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2020-08-21 19:42 [PATCH v6 00/29] Warn on orphan section placement Kees Cook
2020-08-21 19:42 ` [PATCH v6 01/29] vmlinux.lds.h: Create COMMON_DISCARDS Kees Cook
2020-09-01 11:48   ` [tip: core/build] " tip-bot2 for Kees Cook
2020-08-21 19:42 ` [PATCH v6 02/29] vmlinux.lds.h: Add .gnu.version* to COMMON_DISCARDS Kees Cook
2020-09-01 11:48   ` [tip: core/build] " tip-bot2 for Kees Cook
2020-08-21 19:42 ` [PATCH v6 03/29] vmlinux.lds.h: Avoid KASAN and KCSAN's unwanted sections Kees Cook
2020-09-01 11:48   ` [tip: core/build] " tip-bot2 for Kees Cook
2020-08-21 19:42 ` [PATCH v6 04/29] vmlinux.lds.h: Split ELF_DETAILS from STABS_DEBUG Kees Cook
2020-09-01 11:48   ` [tip: core/build] " tip-bot2 for Kees Cook
2020-08-21 19:42 ` [PATCH v6 05/29] vmlinux.lds.h: Add .symtab, .strtab, and .shstrtab to ELF_DETAILS Kees Cook
2020-09-01 11:47   ` [tip: core/build] " tip-bot2 for Kees Cook
2020-08-21 19:42 ` Kees Cook [this message]
2020-09-01 11:47   ` [tip: core/build] vmlinux.lds.h: Add PGO and AutoFDO input sections tip-bot2 for Nick Desaulniers
2020-08-21 19:42 ` [PATCH v6 07/29] efi/libstub: Disable -mbranch-protection Kees Cook
2020-09-01 11:47   ` [tip: core/build] " tip-bot2 for Kees Cook
2020-08-21 19:42 ` [PATCH v6 08/29] arm64/mm: Remove needless section quotes Kees Cook
2020-09-01 11:47   ` [tip: core/build] " tip-bot2 for Kees Cook
2020-08-21 19:42 ` [PATCH v6 09/29] arm64/kernel: Remove needless Call Frame Information annotations Kees Cook
2020-09-01 11:47   ` [tip: core/build] " tip-bot2 for Kees Cook
2020-08-21 19:42 ` [PATCH v6 10/29] arm64/build: Remove .eh_frame* sections due to unwind tables Kees Cook
2020-09-01 11:47   ` [tip: core/build] " tip-bot2 for Kees Cook
2020-08-21 19:42 ` [PATCH v6 11/29] arm64/build: Use common DISCARDS in linker script Kees Cook
2020-09-01 11:47   ` [tip: core/build] " tip-bot2 for Kees Cook
2020-08-21 19:42 ` [PATCH v6 12/29] arm64/build: Add missing DWARF sections Kees Cook
2020-09-01 11:47   ` [tip: core/build] " tip-bot2 for Kees Cook
2020-08-21 19:42 ` [PATCH v6 13/29] arm64/build: Assert for unwanted sections Kees Cook
2020-09-01 11:47   ` [tip: core/build] " tip-bot2 for Kees Cook
2020-10-26 12:29   ` [PATCH v6 13/29] " Geert Uytterhoeven
2020-10-26 13:29     ` Geert Uytterhoeven
2020-10-26 16:01       ` Geert Uytterhoeven
2020-10-26 17:38         ` Ard Biesheuvel
2020-10-26 17:43           ` Geert Uytterhoeven
2020-10-26 17:48             ` Nick Desaulniers
2020-10-26 17:53               ` Geert Uytterhoeven
2020-10-27  8:37                 ` Geert Uytterhoeven
2020-10-27 19:25               ` Geert Uytterhoeven
2020-10-27 19:33                 ` Ard Biesheuvel
2020-10-27 20:00                   ` Arvind Sankar
2020-10-27 20:12                 ` Nick Desaulniers
2020-10-27 20:15                   ` Ard Biesheuvel
2020-10-27 20:17                     ` Nick Desaulniers
2020-10-27 20:30                       ` Arvind Sankar
2020-10-27 20:40                         ` Nick Desaulniers
2020-10-27 21:24                           ` Arvind Sankar
2020-10-27 20:28                     ` Nick Desaulniers
2020-10-27 20:32                       ` Arvind Sankar
2020-10-27 20:36                         ` Nick Desaulniers
2020-10-28 21:36                     ` Alexei Starovoitov
2020-10-27  8:51             ` Geert Uytterhoeven
2020-10-27 10:08           ` Jean-Philippe Brucker
2020-10-27 10:20             ` Geert Uytterhoeven
2020-10-27 11:29               ` Ard Biesheuvel
2020-10-27 11:53                 ` Naresh Kamboju
2020-10-27 13:56                 ` Ard Biesheuvel
2020-08-21 19:42 ` [PATCH v6 14/29] arm64/build: Warn on orphan section placement Kees Cook
2020-08-21 19:42 ` [PATCH v6 15/29] arm/build: Refactor linker script headers Kees Cook
2020-09-01 11:47   ` [tip: core/build] " tip-bot2 for Kees Cook
2020-08-21 19:42 ` [PATCH v6 16/29] arm/build: Explicitly keep .ARM.attributes sections Kees Cook
2020-09-01 11:47   ` [tip: core/build] " tip-bot2 for Kees Cook
2020-08-21 19:42 ` [PATCH v6 17/29] arm/build: Add missing sections Kees Cook
2020-09-01 11:47   ` [tip: core/build] " tip-bot2 for Kees Cook
2020-08-21 19:42 ` [PATCH v6 18/29] arm/build: Assert for unwanted sections Kees Cook
2020-09-01 11:47   ` [tip: core/build] " tip-bot2 for Kees Cook
2020-08-21 19:43 ` [PATCH v6 19/29] arm/build: Warn on orphan section placement Kees Cook
2020-08-21 19:43 ` [PATCH v6 20/29] arm/boot: Handle all sections explicitly Kees Cook
2020-09-01 11:47   ` [tip: core/build] " tip-bot2 for Kees Cook
2020-08-21 19:43 ` [PATCH v6 21/29] arm/boot: Warn on orphan section placement Kees Cook
2020-08-21 19:43 ` [PATCH v6 22/29] x86/asm: Avoid generating unused kprobe sections Kees Cook
2020-09-01 11:47   ` [tip: core/build] " tip-bot2 for Kees Cook
2020-08-21 19:43 ` [PATCH v6 23/29] x86/build: Enforce an empty .got.plt section Kees Cook
2020-09-01 11:47   ` [tip: core/build] " tip-bot2 for Kees Cook
2020-08-21 19:43 ` [PATCH v6 24/29] x86/build: Assert for unwanted sections Kees Cook
2020-09-01 11:47   ` [tip: core/build] x86/build: Add asserts " tip-bot2 for Kees Cook
2020-08-21 19:43 ` [PATCH v6 25/29] x86/build: Warn on orphan section placement Kees Cook
2020-08-21 19:43 ` [PATCH v6 26/29] x86/boot/compressed: Reorganize zero-size section asserts Kees Cook
2020-09-01 11:47   ` [tip: core/build] " tip-bot2 for Kees Cook
2020-08-21 19:43 ` [PATCH v6 27/29] x86/boot/compressed: Remove, discard, or assert for unwanted sections Kees Cook
2020-08-21 20:01   ` Arvind Sankar
2020-08-21 21:21     ` Kees Cook
2020-08-21 21:28       ` Arvind Sankar
2020-09-01 11:47   ` [tip: core/build] " tip-bot2 for Kees Cook
2020-08-21 19:43 ` [PATCH v6 28/29] x86/boot/compressed: Add missing debugging sections to output Kees Cook
2020-09-01 11:47   ` [tip: core/build] " tip-bot2 for Kees Cook
2020-08-21 19:43 ` [PATCH v6 29/29] x86/boot/compressed: Warn on orphan section placement Kees Cook
2020-08-31 19:41 ` [PATCH v6 00/29] " Kees Cook
2020-09-01  7:11   ` Ingo Molnar
2020-09-01  7:59     ` Ingo Molnar
2020-09-01  8:16       ` Ingo Molnar
2020-09-01 15:17         ` Kees Cook
2020-09-01 18:02           ` Nick Desaulniers
2020-09-01 23:18             ` Kees Cook
2020-09-01 23:54               ` Nick Desaulniers

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