linux-kernel - [PATCH] rust: KASAN+RETHUNK requires rustc 1.83.0

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Message-ID: <20240926093849.1192264-1-aliceryhl@google.com>
Date: Thu, 26 Sep 2024 09:38:49 +0000
From: Alice Ryhl <aliceryhl@...gle.com>
To: ojeda@...nel.org
Cc: a.hindborg@...sung.com, alex.gaynor@...il.com, aliceryhl@...gle.com, 
	benno.lossin@...ton.me, bjorn3_gh@...tonmail.com, boqun.feng@...il.com, 
	bp@...en8.de, dave.hansen@...ux.intel.com, gary@...yguo.net, hpa@...or.com, 
	jpoimboe@...nel.org, linux-kernel@...r.kernel.org, masahiroy@...nel.org, 
	mingo@...hat.com, nathan@...nel.org, nicolas@...sle.eu, 
	patches@...ts.linux.dev, peterz@...radead.org, rust-for-linux@...r.kernel.org, 
	tglx@...utronix.de, x86@...nel.org
Subject: [PATCH] rust: KASAN+RETHUNK requires rustc 1.83.0

When enabling both KASAN and RETHUNK, objtool emits the following
warnings:

    rust/core.o: warning: objtool: asan.module_ctor+0x13: 'naked' return found in MITIGATION_RETHUNK build
    rust/core.o: warning: objtool: asan.module_dtor+0x13: 'naked' return found in MITIGATION_RETHUNK build

This is caused by the -Zfunction-return=thunk-extern flag in rustc not
properly informing LLVM about the mitigation, which means that the KASAN
functions asan.module_ctor and asan.module_dtor are generated without
the rethunk mitigation.

The other mitigations that we enabled for Rust (SLS, RETPOLINE) do not
have the same bug, as they're being applied through the target-feature
functionality instead.

This is being fixed for rustc 1.83.0, so update Kconfig to reject this
configuration on older compilers.

Link: https://github.com/rust-lang/rust/pull/130824
Fixes: d7868550d573 ("x86/rust: support MITIGATION_RETHUNK")
Reported-by: Miguel Ojeda <ojeda@...nel.org>
Closes: https://lore.kernel.org/all/CANiq72myZL4_poCMuNFevtpYYc0V0embjSuKb7y=C+m3vVA_8g@mail.gmail.com/
Signed-off-by: Alice Ryhl <aliceryhl@...gle.com>
---
 init/Kconfig | 1 +
 1 file changed, 1 insertion(+)

diff --git a/init/Kconfig b/init/Kconfig
index fa734a144589..9a2bcba426c5 100644
--- a/init/Kconfig
+++ b/init/Kconfig
@@ -1950,6 +1950,7 @@ config RUST
 	select CFI_ICALL_NORMALIZE_INTEGERS if CFI_CLANG
 	depends on !CALL_PADDING || RUSTC_VERSION >= 108100
 	depends on !KASAN_SW_TAGS
+	depends on !(MITIGATION_RETHUNK && KASAN) || RUSTC_VERSION >= 108300
 	help
 	  Enables Rust support in the kernel.
 
-- 
2.46.0.792.g87dc391469-goog