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rust: cfi: add support for CFI_CLANG with Rust

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Make it possible to use the Control Flow Integrity (CFI) sanitizer when
Rust is enabled. Enabling CFI with Rust requires that CFI is configured
to normalize integer types so that all integer types of the same size
and signedness are compatible under CFI.

Rust and C use the same LLVM backend for code generation, so Rust KCFI
is compatible with the KCFI used in the kernel for C. In the case of
FineIBT, CFI also depends on -Zpatchable-function-entry for rewriting
the function prologue, so we set that flag for Rust as well. The flag
for FineIBT requires rustc 1.80.0 or later, so include a Kconfig
requirement for that.

Enabling Rust will select CFI_ICALL_NORMALIZE_INTEGERS because the flag
is required to use Rust with CFI. Using select rather than `depends on`
avoids the case where Rust is not visible in menuconfig due to
CFI_ICALL_NORMALIZE_INTEGERS not being enabled. One disadvantage of
select is that RUST must `depends on` all of the things that
CFI_ICALL_NORMALIZE_INTEGERS depends on to avoid invalid configurations.

Alice has been using KCFI on her phone for several months, so it is
reasonably well tested on arm64.

Signed-off-by: Matthew Maurer <mmaurer@google.com>
Co-developed-by: Alice Ryhl <aliceryhl@google.com>
Signed-off-by: Alice Ryhl <aliceryhl@google.com>
Reviewed-by: Sami Tolvanen <samitolvanen@google.com>
Tested-by: Gatlin Newhouse <gatlin.newhouse@gmail.com>
Acked-by: Kees Cook <kees@kernel.org>
Acked-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Link: https://lore.kernel.org/r/20240801-kcfi-v2-2-c93caed3d121@google.com
[ Replaced `!FINEIBT` requirement with `!CALL_PADDING` to prevent
  a build error on older Rust compilers. Fixed typo. - Miguel ]
Signed-off-by: Miguel Ojeda <ojeda@kernel.org>
This commit is contained in:
Matthew Maurer 2024-09-12 21:00:44 +02:00 committed by Miguel Ojeda
parent ce4a262098
commit ca627e6365
5 changed files with 16 additions and 2 deletions
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7
Makefile
View File

@ -957,6 +957,13 @@ CC_FLAGS_CFI := -fsanitize=kcfi
ifdef CONFIG_CFI_ICALL_NORMALIZE_INTEGERS
CC_FLAGS_CFI += -fsanitize-cfi-icall-experimental-normalize-integers
endif
ifdef CONFIG_RUST
# Always pass -Zsanitizer-cfi-normalize-integers as CONFIG_RUST selects
# CONFIG_CFI_ICALL_NORMALIZE_INTEGERS.
RUSTC_FLAGS_CFI := -Zsanitizer=kcfi -Zsanitizer-cfi-normalize-integers
KBUILD_RUSTFLAGS += $(RUSTC_FLAGS_CFI)
export RUSTC_FLAGS_CFI
endif
KBUILD_CFLAGS += $(CC_FLAGS_CFI)
export CC_FLAGS_CFI
endif

4
arch/x86/Makefile
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@ -242,6 +242,10 @@ ifdef CONFIG_CALL_PADDING
PADDING_CFLAGS := -fpatchable-function-entry=$(CONFIG_FUNCTION_PADDING_BYTES),$(CONFIG_FUNCTION_PADDING_BYTES)
KBUILD_CFLAGS += $(PADDING_CFLAGS)
export PADDING_CFLAGS
PADDING_RUSTFLAGS := -Zpatchable-function-entry=$(CONFIG_FUNCTION_PADDING_BYTES),$(CONFIG_FUNCTION_PADDING_BYTES)
KBUILD_RUSTFLAGS += $(PADDING_RUSTFLAGS)
export PADDING_RUSTFLAGS
endif
KBUILD_LDFLAGS += -m elf_$(UTS_MACHINE)

4
init/Kconfig
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@ -1905,11 +1905,13 @@ config RUST
bool "Rust support"
depends on HAVE_RUST
depends on RUST_IS_AVAILABLE
depends on !CFI_CLANG
depends on !MODVERSIONS
depends on !GCC_PLUGIN_RANDSTRUCT
depends on !RANDSTRUCT
depends on !DEBUG_INFO_BTF || PAHOLE_HAS_LANG_EXCLUDE
depends on !CFI_CLANG || RUSTC_VERSION >= 107900 && $(cc-option,-fsanitize=kcfi -fsanitize-cfi-icall-experimental-normalize-integers)
select CFI_ICALL_NORMALIZE_INTEGERS if CFI_CLANG
depends on !CALL_PADDING || RUSTC_VERSION >= 108000
help
Enables Rust support in the kernel.

2
rust/Makefile
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@ -306,7 +306,7 @@ $(obj)/bindings/bindings_helpers_generated.rs: $(src)/helpers/helpers.c FORCE
quiet_cmd_exports = EXPORTS $@
cmd_exports = \
$(NM) -p --defined-only $< \
| awk '/ (T|R|D) / {printf "EXPORT_SYMBOL_RUST_GPL(%s);\n",$$3}' > $@
| awk '$$2~/(T|R|D)/ && $$3!~/__cfi/ {printf "EXPORT_SYMBOL_RUST_GPL(%s);\n",$$3}' > $@
$(obj)/exports_core_generated.h: $(obj)/core.o FORCE
$(call if_changed,exports)

1
scripts/generate_rust_target.rs
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@ -207,6 +207,7 @@ fn main() {
}
ts.push("features", features);
ts.push("llvm-target", "x86_64-linux-gnu");
ts.push("supported-sanitizers", ["kcfi"]);
ts.push("target-pointer-width", "64");
} else if cfg.has("X86_32") {
// This only works on UML, as i386 otherwise needs regparm support in rustc