linux/tools/objtool, branch v6.15

Merge tag 'its-for-linus-20250509' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip

2025-05-12T00:23:03Z

Pull x86 ITS mitigation from Dave Hansen: "Mitigate Indirect Target Selection (ITS) issue. I'd describe this one as a good old CPU bug where the behavior is _obviously_ wrong, but since it just results in bad predictions it wasn't wrong enough to notice. Well, the researchers noticed and also realized that thus bug undermined a bunch of existing indirect branch mitigations. Thus the unusually wide impact on this one. Details: ITS is a bug in some Intel CPUs that affects indirect branches including RETs in the first half of a cacheline. Due to ITS such branches may get wrongly predicted to a target of (direct or indirect) branch that is located in the second half of a cacheline. Researchers at VUSec found this behavior and reported to Intel. Affected processors: - Cascade Lake, Cooper Lake, Whiskey Lake V, Coffee Lake R, Comet Lake, Ice Lake, Tiger Lake and Rocket Lake. Scope of impact: - Guest/host isolation: When eIBRS is used for guest/host isolation, the indirect branches in the VMM may still be predicted with targets corresponding to direct branches in the guest. - Intra-mode using cBPF: cBPF can be used to poison the branch history to exploit ITS. Realigning the indirect branches and RETs mitigates this attack vector. - User/kernel: With eIBRS enabled user/kernel isolation is *not* impacted by ITS. - Indirect Branch Prediction Barrier (IBPB): Due to this bug indirect branches may be predicted with targets corresponding to direct branches which were executed prior to IBPB. This will be fixed in the microcode. Mitigation: As indirect branches in the first half of cacheline are affected, the mitigation is to replace those indirect branches with a call to thunk that is aligned to the second half of the cacheline. RETs that take prediction from RSB are not affected, but they may be affected by RSB-underflow condition. So, RETs in the first half of cacheline are also patched to a return thunk that executes the RET aligned to second half of cacheline" * tag 'its-for-linus-20250509' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip: selftest/x86/bugs: Add selftests for ITS x86/its: FineIBT-paranoid vs ITS x86/its: Use dynamic thunks for indirect branches x86/ibt: Keep IBT disabled during alternative patching mm/execmem: Unify early execmem_cache behaviour x86/its: Align RETs in BHB clear sequence to avoid thunking x86/its: Add support for RSB stuffing mitigation x86/its: Add "vmexit" option to skip mitigation on some CPUs x86/its: Enable Indirect Target Selection mitigation x86/its: Add support for ITS-safe return thunk x86/its: Add support for ITS-safe indirect thunk x86/its: Enumerate Indirect Target Selection (ITS) bug Documentation: x86/bugs/its: Add ITS documentation

x86/its: FineIBT-paranoid vs ITS

2025-05-09T20:39:36Z

FineIBT-paranoid was using the retpoline bytes for the paranoid check, disabling retpolines, because all parts that have IBT also have eIBRS and thus don't need no stinking retpolines. Except... ITS needs the retpolines for indirect calls must not be in the first half of a cacheline :-/ So what was the paranoid call sequence: : 0: 41 ba 78 56 34 12 mov $0x12345678, %r10d 6: 45 3b 53 f7 cmp -0x9(%r11), %r10d a: 4d 8d 5b lea -0x10(%r11), %r11 e: 75 fd jne d 10: 41 ff d3 call *%r11 13: 90 nop Now becomes: : 0: 41 ba 78 56 34 12 mov $0x12345678, %r10d 6: 45 3b 53 f7 cmp -0x9(%r11), %r10d a: 4d 8d 5b f0 lea -0x10(%r11), %r11 e: 2e e8 XX XX XX XX cs call __x86_indirect_paranoid_thunk_r11 Where the paranoid_thunk looks like: 1d: (bad) __x86_indirect_paranoid_thunk_r11: 1e: 75 fd jne 1d __x86_indirect_its_thunk_r11: 20: 41 ff eb jmp *%r11 23: cc int3 [ dhansen: remove initialization to false ] Signed-off-by: Peter Zijlstra (Intel) Signed-off-by: Pawan Gupta Signed-off-by: Dave Hansen Reviewed-by: Alexandre Chartre

objtool/rust: add one more `noreturn` Rust function for Rust 1.87.0

2025-05-06T22:08:51Z

Starting with Rust 1.87.0 (expected 2025-05-15), `objtool` may report: rust/core.o: warning: objtool: _R..._4core9panicking9panic_fmt() falls through to next function _R..._4core9panicking18panic_nounwind_fmt() rust/core.o: warning: objtool: _R..._4core9panicking18panic_nounwind_fmt() falls through to next function _R..._4core9panicking5panic() The reason is that `rust_begin_unwind` is now mangled: _R..._7___rustc17rust_begin_unwind Thus add the mangled one to the list so that `objtool` knows it is actually `noreturn`. See commit 56d680dd23c3 ("objtool/rust: list `noreturn` Rust functions") for more details. Alternatively, we could remove the fixed one in `noreturn.h` and relax this test to cover both, but it seems best to be strict as long as we can. Cc: stable@vger.kernel.org # Needed in 6.12.y and later (Rust is pinned in older LTSs). Cc: Josh Poimboeuf Cc: Peter Zijlstra Reviewed-by: Alice Ryhl Link: https://lore.kernel.org/r/20250502140237.1659624-2-ojeda@kernel.org Signed-off-by: Miguel Ojeda

Merge tag 'rust-fixes-6.15' of git://git.kernel.org/pub/scm/linux/kernel/git/ojeda/linux

2025-04-19T17:02:43Z

Pull rust fixes from Miguel Ojeda: "Toolchain and infrastructure: - Fix missing KASAN LLVM flags on first build (and fix spurious rebuilds) by skipping '--target' - Fix Make < 4.3 build error by using '$(pound)' - Fix UML build error by removing 'volatile' qualifier from io helpers - Fix UML build error by adding 'dma_{alloc,free}_attrs()' helpers - Clean gendwarfksyms warnings by avoiding to export '__pfx' symbols - Clean objtool warning by adding a new 'noreturn' function for 1.86.0 - Disable 'needless_continue' Clippy lint due to new 1.86.0 warnings - Add missing 'ffi' crate to 'generate_rust_analyzer.py' 'pin-init' crate: - Import a couple fixes from upstream" * tag 'rust-fixes-6.15' of git://git.kernel.org/pub/scm/linux/kernel/git/ojeda/linux: rust: helpers: Add dma_alloc_attrs() and dma_free_attrs() rust: helpers: Remove volatile qualifier from io helpers rust: kbuild: use `pound` to support GNU Make < 4.3 objtool/rust: add one more `noreturn` Rust function for Rust 1.86.0 rust: kasan/kbuild: fix missing flags on first build rust: disable `clippy::needless_continue` rust: kbuild: Don't export __pfx symbols rust: pin-init: use Markdown autolinks in Rust comments rust: pin-init: alloc: restrict `impl ZeroableOption` for `Box` to `T: Sized` scripts: generate_rust_analyzer: Add ffi crate

objtool/rust: add one more `noreturn` Rust function for Rust 1.86.0

2025-04-14T15:02:49Z

Starting with Rust 1.86.0 (see upstream commit b151b513ba2b ("Insert null checks for pointer dereferences when debug assertions are enabled") [1]), under some kernel configurations with `CONFIG_RUST_DEBUG_ASSERTIONS=y`, one may trigger a new `objtool` warning: rust/kernel.o: warning: objtool: _R..._6kernel9workqueue6system() falls through to next function _R...9workqueue14system_highpri() due to a call to the `noreturn` symbol: core::panicking::panic_null_pointer_dereference Thus add it to the list so that `objtool` knows it is actually `noreturn`. See commit 56d680dd23c3 ("objtool/rust: list `noreturn` Rust functions") for more details. Cc: stable@vger.kernel.org # Needed in 6.12.y and later (Rust is pinned in older LTSs). Fixes: 56d680dd23c3 ("objtool/rust: list `noreturn` Rust functions") Link: https://github.com/rust-lang/rust/commit/b151b513ba2b65c7506ec1a80f2712bbd09154d1 [1] Reviewed-by: Alice Ryhl Link: https://lore.kernel.org/r/20250413002338.1741593-1-ojeda@kernel.org Signed-off-by: Miguel Ojeda

objtool: Fix false-positive "ignoring unreachables" warning

2025-04-10T20:55:00Z

There's no need to try to automatically disable unreachable warnings if they've already been manually disabled due to CONFIG_KCOV quirks. This avoids a spurious warning with a KCOV kernel: fs/smb/client/cifs_unicode.o: warning: objtool: cifsConvertToUTF16.part.0+0xce5: ignoring unreachables due to jump table quirk Fixes: eeff7ac61526 ("objtool: Warn when disabling unreachable warnings") Reported-by: kernel test robot Signed-off-by: Josh Poimboeuf Signed-off-by: Ingo Molnar Link: https://lore.kernel.org/r/5eb28eeb6a724b7d945a961cfdcf8d41e6edf3dc.1744238814.git.jpoimboe@kernel.org Closes: https://lore.kernel.org/r/202504090910.QkvTAR36-lkp@intel.com/

objtool: Remove ANNOTATE_IGNORE_ALTERNATIVE from CLAC/STAC

2025-04-08T20:03:51Z

ANNOTATE_IGNORE_ALTERNATIVE adds additional noise to the code generated by CLAC/STAC alternatives, hurting readability for those whose read uaccess-related code generation on a regular basis. Remove the annotation specifically for the "NOP patched with CLAC/STAC" case in favor of a manual check. Leave the other uses of that annotation in place as they're less common and more difficult to detect. Suggested-by: Linus Torvalds Signed-off-by: Josh Poimboeuf Signed-off-by: Ingo Molnar Acked-by: Linus Torvalds Link: https://lore.kernel.org/r/fc972ba4995d826fcfb8d02733a14be8d670900b.1744098446.git.jpoimboe@kernel.org

objtool, xen: Fix INSN_SYSCALL / INSN_SYSRET semantics

2025-04-08T07:14:12Z

Objtool uses an arbitrary rule for INSN_SYSCALL and INSN_SYSRET that almost works by accident: if it's in a function, control flow continues after the instruction, otherwise it terminates. That behavior should instead be based on the semantics of the underlying instruction. Change INSN_SYSCALL to always preserve control flow and INSN_SYSRET to always terminate it. The changed semantic for INSN_SYSCALL requires a tweak to the !CONFIG_IA32_EMULATION version of xen_entry_SYSCALL_compat(). In Xen, SYSCALL is a hypercall which usually returns. But in this case it's a hypercall to IRET which doesn't return. Add UD2 to tell objtool to terminate control flow, and to prevent undefined behavior at runtime. Signed-off-by: Josh Poimboeuf Signed-off-by: Ingo Molnar Reviewed-by: Juergen Gross # for the Xen part Cc: Linus Torvalds Link: https://lore.kernel.org/r/19453dfe9a0431b7f016e9dc16d031cad3812a50.1744095216.git.jpoimboe@kernel.org

objtool: Stop UNRET validation on UD2

2025-04-08T07:14:11Z

In preparation for simplifying INSN_SYSCALL, make validate_unret() terminate control flow on UD2 just like validate_branch() already does. Signed-off-by: Josh Poimboeuf Signed-off-by: Ingo Molnar Cc: Linus Torvalds Link: https://lore.kernel.org/r/ce841269e7e28c8b7f32064464a9821034d724ff.1744095216.git.jpoimboe@kernel.org

objtool: Split INSN_CONTEXT_SWITCH into INSN_SYSCALL and INSN_SYSRET

2025-04-08T07:14:11Z

INSN_CONTEXT_SWITCH is ambiguous. It can represent both call semantics (SYSCALL, SYSENTER) and return semantics (SYSRET, IRET, RETS, RETU). Those differ significantly: calls preserve control flow whereas returns terminate it. Objtool uses an arbitrary rule for INSN_CONTEXT_SWITCH that almost works by accident: if in a function, keep going; otherwise stop. It should instead be based on the semantics of the underlying instruction. In preparation for improving that, split INSN_CONTEXT_SWITCH into INSN_SYCALL and INSN_SYSRET. No functional change. Signed-off-by: Josh Poimboeuf Signed-off-by: Ingo Molnar Cc: Linus Torvalds Link: https://lore.kernel.org/r/19a76c74d2c051d3bc9a775823cafc65ad267a7a.1744095216.git.jpoimboe@kernel.org