In preparation for adding Clang sanitizer coverage stack depth tracking
that can support stack depth callbacks:
- Add the new top-level CONFIG_KSTACK_ERASE option which will be
implemented either with the stackleak GCC plugin, or with the Clang
stack depth callback support.
- Rename CONFIG_GCC_PLUGIN_STACKLEAK as needed to CONFIG_KSTACK_ERASE,
but keep it for anything specific to the GCC plugin itself.
- Rename all exposed "STACKLEAK" names and files to "KSTACK_ERASE" (named
for what it does rather than what it protects against), but leave as
many of the internals alone as possible to avoid even more churn.
While here, also split "prev_lowest_stack" into CONFIG_KSTACK_ERASE_METRICS,
since that's the only place it is referenced from.
Suggested-by: Ingo Molnar <mingo@kernel.org>
Link: https://lore.kernel.org/r/20250717232519.2984886-1-kees@kernel.org
Signed-off-by: Kees Cook <kees@kernel.org>
Pull compiler version requirement update from Arnd Bergmann:
"Require gcc-8 and binutils-2.30
x86 already uses gcc-8 as the minimum version, this changes all other
architectures to the same version. gcc-8 is used is Debian 10 and Red
Hat Enterprise Linux 8, both of which are still supported, and
binutils 2.30 is the oldest corresponding version on those.
Ubuntu Pro 18.04 and SUSE Linux Enterprise Server 15 both use gcc-7 as
the system compiler but additionally include toolchains that remain
supported.
With the new minimum toolchain versions, a number of workarounds for
older versions can be dropped, in particular on x86_64 and arm64.
Importantly, the updated compiler version allows removing two of the
five remaining gcc plugins, as support for sancov and structeak
features is already included in modern compiler versions.
I tried collecting the known changes that are possible based on the
new toolchain version, but expect that more cleanups will be possible.
Since this touches multiple architectures, I merged the patches
through the asm-generic tree."
* tag 'gcc-minimum-version-6.16' of git://git.kernel.org/pub/scm/linux/kernel/git/arnd/asm-generic:
Makefile.kcov: apply needed compiler option unconditionally in CFLAGS_KCOV
Documentation: update binutils-2.30 version reference
gcc-plugins: remove SANCOV gcc plugin
Kbuild: remove structleak gcc plugin
arm64: drop binutils version checks
raid6: skip avx512 checks
kbuild: require gcc-8 and binutils-2.30
There was no dependency between the plugins changing and the rest of the
kernel being built. This could cause strange behaviors as instrumentation
could vary between targets depending on when they were built.
Generate a new header file, gcc-plugins.h, any time the GCC plugins
change. Include the header file in compiler-version.h when its associated
feature name, GCC_PLUGINS, is defined. This will be picked up by fixdep
and force rebuilds where needed.
Add a generic "touch" kbuild command, which will be used again in
a following patch. Add a "normalize_path" string helper to make the
"TOUCH" output less ugly.
Link: https://lore.kernel.org/r/20250503184623.2572355-1-kees@kernel.org
Tested-by: Nicolas Schier <n.schier@avm.de>
Reviewed-by: Nicolas Schier <n.schier@avm.de>
Signed-off-by: Kees Cook <kees@kernel.org>
With the minimum gcc version raised to 8.1, all supported compilers
now understand the -fsanitize-coverage=trace-pc option, and there
is no longer a need for the separate compiler plugin.
Since only gcc-5 was able to use the plugin for several year now,
it was already likely unused.
Signed-off-by: Arnd Bergmann <arnd@arndb.de>
gcc-12 and higher support the -ftrivial-auto-var-init= flag, after
gcc-8 is the minimum version, this is half of the supported ones, and
the vast majority of the versions that users are actually likely to
have, so it seems like a good time to stop having the fallback
plugin implementation
Older toolchains are still able to build kernels normally without
this plugin, but won't be able to use variable initialization..
Signed-off-by: Arnd Bergmann <arnd@arndb.de>
Commit 36d4b36b69 ("lib/nodemask: inline next_node_in() and
node_random()") refactored some code by moving node_random() from
lib/nodemask.c to include/linux/nodemask.h, thus requiring nodemask.h to
include random.h, which conditionally defines add_latent_entropy()
depending on whether the macro LATENT_ENTROPY_PLUGIN is defined.
This broke the build on powerpc, where nodemask.h is indirectly included
in arch/powerpc/kernel/prom_init.c, part of the early boot machinery that
is excluded from the latent entropy plugin using
DISABLE_LATENT_ENTROPY_PLUGIN. It turns out that while we add a gcc flag
to disable the actual plugin, we don't undefine LATENT_ENTROPY_PLUGIN.
This leads to the following:
CC arch/powerpc/kernel/prom_init.o
In file included from ./include/linux/nodemask.h:97,
from ./include/linux/mmzone.h:17,
from ./include/linux/gfp.h:7,
from ./include/linux/xarray.h:15,
from ./include/linux/radix-tree.h:21,
from ./include/linux/idr.h:15,
from ./include/linux/kernfs.h:12,
from ./include/linux/sysfs.h:16,
from ./include/linux/kobject.h:20,
from ./include/linux/pci.h:35,
from arch/powerpc/kernel/prom_init.c:24:
./include/linux/random.h: In function 'add_latent_entropy':
./include/linux/random.h:25:46: error: 'latent_entropy' undeclared (first use in this function); did you mean 'add_latent_entropy'?
25 | add_device_randomness((const void *)&latent_entropy, sizeof(latent_entropy));
| ^~~~~~~~~~~~~~
| add_latent_entropy
./include/linux/random.h:25:46: note: each undeclared identifier is reported only once for each function it appears in
make[2]: *** [scripts/Makefile.build:249: arch/powerpc/kernel/prom_init.o] Fehler 1
make[1]: *** [scripts/Makefile.build:465: arch/powerpc/kernel] Fehler 2
make: *** [Makefile:1855: arch/powerpc] Error 2
Change the DISABLE_LATENT_ENTROPY_PLUGIN flags to undefine
LATENT_ENTROPY_PLUGIN for files where the plugin is disabled.
Cc: Yury Norov <yury.norov@gmail.com>
Fixes: 38addce8b6 ("gcc-plugins: Add latent_entropy plugin")
Link: https://bugzilla.kernel.org/show_bug.cgi?id=216367
Link: https://lore.kernel.org/linuxppc-dev/alpine.DEB.2.22.394.2208152006320.289321@ramsan.of.borg/
Reported-by: Erhard Furtner <erhard_f@mailbox.org>
Signed-off-by: Andrew Donnellan <ajd@linux.ibm.com>
Reviewed-by: Yury Norov <yury.norov@gmail.com>
Signed-off-by: Kees Cook <keescook@chromium.org>
Link: https://lore.kernel.org/r/20220816051720.44108-1-ajd@linux.ibm.com
In order to compare instrumentation between builds, make the verbose
mode of the plugin available during the build. This is rarely needed
(behind EXPERT) and very noisy (disabled for COMPILE_TEST).
Cc: Alexander Popov <alex.popov@linux.com>
Signed-off-by: Kees Cook <keescook@chromium.org>
Pull compiler hardening updates from Kees Cook:
"These are various compiler-related hardening feature updates. Notable
is the addition of an explicit limited rationale for, and deprecation
schedule of, gcc-plugins.
gcc-plugins:
- remove support for GCC 4.9 and older (Ard Biesheuvel)
- remove duplicate include in gcc-common.h (Ye Guojin)
- Explicitly document purpose and deprecation schedule (Kees Cook)
- Remove cyc_complexity (Kees Cook)
instrumentation:
- Avoid harmless Clang option under CONFIG_INIT_STACK_ALL_ZERO (Kees Cook)
Clang LTO:
- kallsyms: strip LTO suffixes from static functions (Nick Desaulniers)"
* tag 'hardening-v5.16-rc1' of git://git.kernel.org/pub/scm/linux/kernel/git/kees/linux:
gcc-plugins: remove duplicate include in gcc-common.h
gcc-plugins: Remove cyc_complexity
gcc-plugins: Explicitly document purpose and deprecation schedule
kallsyms: strip LTO suffixes from static functions
gcc-plugins: remove support for GCC 4.9 and older
hardening: Avoid harmless Clang option under CONFIG_INIT_STACK_ALL_ZERO
The kernel code instrumentation in stackleak gcc plugin works in two stages.
At first, stack tracking is added to GIMPLE representation of every function
(except some special cases). And later, when stack frame size info is
available, stack tracking is removed from the RTL representation of the
functions with small stack frame. There is an unwanted side-effect for these
functions: some of them do useless work with caller-saved registers.
As an example of such case, proc_sys_write without() instrumentation:
55 push %rbp
41 b8 01 00 00 00 mov $0x1,%r8d
48 89 e5 mov %rsp,%rbp
e8 11 ff ff ff callq ffffffff81284610 <proc_sys_call_handler>
5d pop %rbp
c3 retq
0f 1f 44 00 00 nopl 0x0(%rax,%rax,1)
66 2e 0f 1f 84 00 00 nopw %cs:0x0(%rax,%rax,1)
00 00 00
proc_sys_write() with instrumentation:
55 push %rbp
48 89 e5 mov %rsp,%rbp
41 56 push %r14
41 55 push %r13
41 54 push %r12
53 push %rbx
49 89 f4 mov %rsi,%r12
48 89 fb mov %rdi,%rbx
49 89 d5 mov %rdx,%r13
49 89 ce mov %rcx,%r14
4c 89 f1 mov %r14,%rcx
4c 89 ea mov %r13,%rdx
4c 89 e6 mov %r12,%rsi
48 89 df mov %rbx,%rdi
41 b8 01 00 00 00 mov $0x1,%r8d
e8 f2 fe ff ff callq ffffffff81298e80 <proc_sys_call_handler>
5b pop %rbx
41 5c pop %r12
41 5d pop %r13
41 5e pop %r14
5d pop %rbp
c3 retq
66 0f 1f 84 00 00 00 nopw 0x0(%rax,%rax,1)
00 00
Let's improve the instrumentation to avoid this:
1. Make stackleak_track_stack() save all register that it works with.
Use no_caller_saved_registers attribute for that function. This attribute
is available for x86_64 and i386 starting from gcc-7.
2. Insert calling stackleak_track_stack() in asm:
asm volatile("call stackleak_track_stack" :: "r" (current_stack_pointer))
Here we use ASM_CALL_CONSTRAINT trick from arch/x86/include/asm/asm.h.
The input constraint is taken into account during gcc shrink-wrapping
optimization. It is needed to be sure that stackleak_track_stack() call is
inserted after the prologue of the containing function, when the stack
frame is prepared.
This work is a deep reengineering of the idea described on grsecurity blog
https://grsecurity.net/resolving_an_unfortunate_stackleak_interaction
Signed-off-by: Alexander Popov <alex.popov@linux.com>
Acked-by: Miguel Ojeda <miguel.ojeda.sandonis@gmail.com>
Link: https://lore.kernel.org/r/20200624123330.83226-5-alex.popov@linux.com
Signed-off-by: Kees Cook <keescook@chromium.org>
This adjusts structleak to also work with non-struct types when they
are passed by reference, since those variables may leak just like
anything else. This is exposed via an improved set of Kconfig options.
(This does mean structleak is slightly misnamed now.)
Building with CONFIG_GCC_PLUGIN_STRUCTLEAK_BYREF_ALL should give the
kernel complete initialization coverage of all stack variables passed
by reference, including padding (see lib/test_stackinit.c).
Using CONFIG_GCC_PLUGIN_STRUCTLEAK_VERBOSE to count added initializations
under defconfig:
..._BYREF: 5945 added initializations
..._BYREF_ALL: 16606 added initializations
There is virtually no change to text+data size (both have less than 0.05%
growth):
text data bss dec hex filename
19502103 5051456 1917000 26470559 193e89f vmlinux.stock
19513412 5051456 1908808 26473676 193f4cc vmlinux.byref
19516974 5047360 1900616 26464950 193d2b6 vmlinux.byref_all
The measured performance difference is in the noise for hackbench and
kernel build benchmarks:
Stock:
5x hackbench -g 20 -l 1000
Mean: 10.649s
Std Dev: 0.339
5x kernel build (4-way parallel)
Mean: 261.98s
Std Dev: 1.53
CONFIG_GCC_PLUGIN_STRUCTLEAK_BYREF:
5x hackbench -g 20 -l 1000
Mean: 10.540s
Std Dev: 0.233
5x kernel build (4-way parallel)
Mean: 260.52s
Std Dev: 1.31
CONFIG_GCC_PLUGIN_STRUCTLEAK_BYREF_ALL:
5x hackbench -g 20 -l 1000
Mean: 10.320
Std Dev: 0.413
5x kernel build (4-way parallel)
Mean: 260.10
Std Dev: 0.86
This does not yet solve missing padding initialization for structures
on the stack that are never passed by reference (which should be a tiny
minority). Hopefully this will be more easily addressed by upstream
compiler fixes after clarifying the C11 padding initialization
specification.
Signed-off-by: Kees Cook <keescook@chromium.org>
Reviewed-by: Ard Biesheuvel <ard.biesheuvel@linaro.org>
On ARM, we currently only change the value of the stack canary when
switching tasks if the kernel was built for UP. On SMP kernels, this
is impossible since the stack canary value is obtained via a global
symbol reference, which means
a) all running tasks on all CPUs must use the same value
b) we can only modify the value when no kernel stack frames are live
on any CPU, which is effectively never.
So instead, use a GCC plugin to add a RTL pass that replaces each
reference to the address of the __stack_chk_guard symbol with an
expression that produces the address of the 'stack_canary' field
that is added to struct thread_info. This way, each task will use
its own randomized value.
Cc: Russell King <linux@armlinux.org.uk>
Cc: Kees Cook <keescook@chromium.org>
Cc: Emese Revfy <re.emese@gmail.com>
Cc: Arnd Bergmann <arnd@arndb.de>
Cc: Laura Abbott <labbott@redhat.com>
Cc: kernel-hardening@lists.openwall.com
Acked-by: Nicolas Pitre <nico@linaro.org>
Signed-off-by: Ard Biesheuvel <ard.biesheuvel@linaro.org>
Signed-off-by: Kees Cook <keescook@chromium.org>
Now that 'archprepare' depends on 'scripts', Kbuild can descend into
scripts/gcc-plugins in a more standard way.
Signed-off-by: Masahiro Yamada <yamada.masahiro@socionext.com>
Reviewed-by: Kees Cook <keescook@chromium.org>
The STACKLEAK feature erases the kernel stack before returning from
syscalls. That reduces the information which kernel stack leak bugs can
reveal and blocks some uninitialized stack variable attacks.
This commit introduces the STACKLEAK gcc plugin. It is needed for
tracking the lowest border of the kernel stack, which is important
for the code erasing the used part of the kernel stack at the end
of syscalls (comes in a separate commit).
The STACKLEAK feature is ported from grsecurity/PaX. More information at:
https://grsecurity.net/https://pax.grsecurity.net/
This code is modified from Brad Spengler/PaX Team's code in the last
public patch of grsecurity/PaX based on our understanding of the code.
Changes or omissions from the original code are ours and don't reflect
the original grsecurity/PaX code.
Signed-off-by: Alexander Popov <alex.popov@linux.com>
Tested-by: Laura Abbott <labbott@redhat.com>
Signed-off-by: Kees Cook <keescook@chromium.org>
The layout of Makefile.gcc-plugins had uneven tabs, and the long names
of things made this file a bit hard to quickly visually parse. This
breaks lines and moves options to the same tab depth. While we're at
it, this also adds some comments about the various sections.
Signed-off-by: Kees Cook <keescook@chromium.org>
GCC_PLUGIN_SUBDIR has never been used. If you really need this in
the future, please re-add it then.
For now, the code is unused. Remove.
'export HOSTLIBS' is not necessary either.
Signed-off-by: Masahiro Yamada <yamada.masahiro@socionext.com>
Signed-off-by: Kees Cook <keescook@chromium.org>
Run scripts/gcc-plugin.sh from Kconfig so that users can enable
GCC_PLUGINS only when the compiler supports building plugins.
Kconfig defines a new symbol, PLUGIN_HOSTCC. This will contain
the compiler (g++ or gcc) used for building plugins, or empty
if the plugin can not be supported at all.
This allows us to remove all ugly testing in Makefile.gcc-plugins.
Signed-off-by: Masahiro Yamada <yamada.masahiro@socionext.com>
Acked-by: Kees Cook <keescook@chromium.org>
For PowerPC, GCC 5.2 is the requirement for GCC plugins. Move the
version check to Kconfig so that the GCC plugin menus will be hidden
if an older compiler is in use.
Signed-off-by: Masahiro Yamada <yamada.masahiro@socionext.com>
Acked-by: Andrew Donnellan <andrew.donnellan@au1.ibm.com>
Reviewed-by: Kees Cook <keescook@chromium.org>
