-mbranch-protection=bti (aarch64) to hardening flags
#28459
This is a simpler (less hardening) version of #24123.
You can inspect binaries using readelf -n, and look for BTI in a .note.gnu.property. i.e
0readelf -n src/bitcoin-cli
1
2Displaying notes found in: .note.gnu.property
3 Owner Data size Description
4 GNU 0x00000010 NT_GNU_PROPERTY_TYPE_0
5 Properties: AArch64 feature: BTI
Related to #19075.
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| Type | Reviewers |
|---|---|
| ACK | TheCharlatan |
| Concept ACK | theuni |
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Concept ACK.
Discussed briefly with @TheCharlatan this morning.
Is there a way to check the resulted binaries that the applied flag actually has effect?
From lwn “The idea is simple enough: if BTI is enabled, the first instruction encountered after an indirect jump must be a special BTI instruction.”
Sounds like it should be testable with an asm dump.
964@@ -965,6 +965,11 @@ if test "$use_hardening" != "no"; then
965 ;;
966 esac
967
968+ case $host in
969+ *aarch64-apple*)
970+ AX_CHECK_COMPILE_FLAG([-mbranch-protection=bti], [HARDENED_CXXFLAGS="$HARDENED_CXXFLAGS -mbranch-protection=bti"])
Why constrain this to apple?
Can we move it up above and just let it fail when unsupported? According to the link above “That instruction is a no-op on systems without BTI”.
Why constrain this to apple?
Not to apple, but I guess one reason to scope this (to aarch64) would be to avoid Wunused-command-line-argument warnings on x86_64. Which now appear in the CI (https://github.com/bitcoin/bitcoin/actions/runs/6381638188/job/17318511090?pr=28459#step:7:1979):
0 CXX libbitcoin_node_a-deploymentstatus.o
1clang: error: argument unused during compilation: '-mbranch-protection=bti' [-Werror,-Wunused-command-line-argument]
This is a simpler (less hardening) version of #24123.
Scoped to aarch64 to avoid unused command line option warnings when
building on x86_64.
Related to #19075.
