-Zharden-sls flag (target modifier) added to enable mitigation against straight line speculation (SLS) by azhogin · Pull Request #136597 · rust-lang/rust

azhogin · 2025-02-05T18:23:38Z

Flag (target modifier) to mitigate against straight line speculation (SLS).
-Zharden-sls=[none|all|return|indirect-jmp].

The flag enables the related features: +harden-sls-ijmp,+harden-sls-ret.
The flag is tracked as a target modifier to be equal between linked crates.

Tracking issue: #116851

rustbot · 2025-02-05T18:23:47Z

r? @estebank

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rustbot · 2025-02-25T17:35:40Z

Some changes occurred in compiler/rustc_codegen_gcc

cc @antoyo, @GuillaumeGomez

klensy · 2025-02-25T18:19:58Z

First commit adds retpoline feature, but PR descriptions says about sls.

azhogin · 2025-02-25T18:24:29Z

First commit adds retpoline feature, but PR descriptions says about sls.

Yes, first commit is in another PR #135927.
This one depends on.

Dylan-DPC · 2025-03-22T17:37:13Z

Marking this as blocked on #135927

Darksonn · 2025-04-28T14:40:49Z

I filed an MCP for this flag: rust-lang/compiler-team#869

bors · 2025-05-18T20:18:00Z

☔ The latest upstream changes (presumably #141232) made this pull request unmergeable. Please resolve the merge conflicts.

workingjubilee · 2025-06-14T01:33:22Z

+warning: target feature `retpoline-external-thunk` cannot be enabled with `-Ctarget-feature`: use `x86-retpoline` target modifier flag instead
+   |
+   = note: this was previously accepted by the compiler but is being phased out; it will become a hard error in a future release!
+   = note: for more information, see issue #116344 <https://github.com/rust-lang/rust/issues/116344>
+
+warning: 1 warning emitted


Why is this possible at all?

workingjubilee · 2025-06-14T01:33:41Z

+//@ compile-flags: --target=x86_64-unknown-linux-gnu --crate-type=lib
+//@ needs-llvm-components: x86
+//@ [by_flag]compile-flags: -Zharden-sls=all
+//@ [by_feature]compile-flags: -Ctarget-feature=+harden-sls-ijmp,+harden-sls-ret


These should not be set by -Ctarget-feature.

@azhogin it would be great if we could make these hard errors now instead of an FCW

Changed to be hard error. Also it requires to add non-aux-compiler-flags directive for tests (related issue described here #147881). To workaround error generated at minicore auxiliary build.

ojeda · 2025-07-16T19:02:02Z

@azhogin Since #135927 is merged now, should this be rebased and unblocked now?

Thanks!

rustbot · 2025-12-03T21:20:04Z

Reminder, once the PR becomes ready for a review, use @rustbot ready.

bors · 2025-12-10T13:36:25Z

☔ The latest upstream changes (presumably #149836) made this pull request unmergeable. Please resolve the merge conflicts.

tomassedovic · 2026-01-27T17:38:02Z

@azhogin just making sure you've seen this, the PR is now waiting on you to address this comment from 2025-12-03: #136597 (comment)

azhogin · 2026-01-29T02:55:30Z

Rebased on cherry-picked wesleywiser's commit "Allow forbidden target features to be hard errors".
Harden-sls produces hard error.

@rustbot ready

rustbot · 2026-05-05T15:54:29Z

This PR was rebased onto a different main commit. Here's a range-diff highlighting what actually changed.

Rebasing is a normal part of keeping PRs up to date, so no action is needed—this note is just to help reviewers.

…t straight line speculation (SLS)

azhogin · 2026-05-05T20:19:03Z

@rustbot review

@workingjubilee

…feature_hard_error_option, r=dingxiangfei2009 Allow forbidden target features to be hard errors Sometimes when adding a new target features to the list of known target features, we want to completely forbid them from being used because they are ABI affecting and should be target modifiers instead. As such, we want to issue an error rather than a warning since there are no future compatibility concerns . r? @workingjubilee since you're familiar with the motivating case in rust-lang#136597 If I rebase that PR on top of this locally, then we get the following error messages when trying to activate the SLS target feature (note that they are *errors* not *warnings* and we've omitted the usual note about future compatibility): ``` error: target feature `harden-sls-ijmp` cannot be enabled with `-Ctarget-feature`: use `harden-sls` compiler flag instead error: target feature `harden-sls-ret` cannot be enabled with `-Ctarget-feature`: use `harden-sls` compiler flag instead error: aborting due to 2 previous errors ```

rust-bors · 2026-05-22T18:14:09Z

☔ The latest upstream changes (presumably #156834) made this pull request unmergeable. Please resolve the merge conflicts.

rustbot assigned estebank Feb 5, 2025

rustbot added S-waiting-on-review Status: Awaiting review from the assignee but also interested parties. T-compiler Relevant to the compiler team, which will review and decide on the PR/issue. labels Feb 5, 2025

azhogin force-pushed the azhogin/sls branch from 821c2d7 to ee66db5 Compare February 6, 2025 19:37

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azhogin force-pushed the azhogin/sls branch from ee66db5 to b5a512c Compare February 8, 2025 11:56

azhogin mentioned this pull request Feb 13, 2025

[RFC] Target Modifiers rust-lang/rfcs#3716

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Darksonn mentioned this pull request Feb 13, 2025

Tracking Issue for target modifiers #136966

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15 tasks

ojeda mentioned this pull request Feb 13, 2025

rustc wanted features & bugfixes Rust-for-Linux/linux#355

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azhogin marked this pull request as ready for review February 25, 2025 17:35

azhogin marked this pull request as draft February 25, 2025 18:23

azhogin mentioned this pull request Feb 25, 2025

retpoline and retpoline-external-thunk flags (target modifiers) to enable retpoline-related target features #135927

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briansmith mentioned this pull request Mar 12, 2025

Support mitigations that are normally done automatically by compilers in assembly briansmith/ring#2479

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Dylan-DPC added S-blocked Status: Blocked on something else such as an RFC or other implementation work. and removed S-waiting-on-review Status: Awaiting review from the assignee but also interested parties. labels Mar 22, 2025

workingjubilee requested changes Jun 14, 2025

View reviewed changes

Comment thread tests/ui/target-feature/retpoline-target-feature-flag.rs Outdated

workingjubilee requested changes Jun 14, 2025

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workingjubilee self-assigned this Jun 14, 2025

Darksonn added S-waiting-on-author Status: This is awaiting some action (such as code changes or more information) from the author. and removed S-blocked Status: Blocked on something else such as an RFC or other implementation work. labels Jul 16, 2025

azhogin force-pushed the azhogin/sls branch from b5a512c to a6f8d63 Compare July 20, 2025 09:56

rustbot added the A-LLVM Area: Code generation parts specific to LLVM. Both correctness bugs and optimization-related issues. label Jul 20, 2025

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azhogin force-pushed the azhogin/sls branch from 692e17d to 99b405a Compare January 29, 2026 02:42

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wesleywiser mentioned this pull request Feb 18, 2026

Allow forbidden target features to be hard errors #152821

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-Zharden-sls flag (target modifier) added to enable mitigation agains…

720aa1f

…t straight line speculation (SLS)

azhogin force-pushed the azhogin/sls branch from 621e1e5 to 720aa1f Compare May 5, 2026 17:09

rustbot added S-waiting-on-review Status: Awaiting review from the assignee but also interested parties. and removed S-waiting-on-author Status: This is awaiting some action (such as code changes or more information) from the author. labels May 5, 2026

wesleywiser added S-waiting-on-author Status: This is awaiting some action (such as code changes or more information) from the author. and removed S-waiting-on-review Status: Awaiting review from the assignee but also interested parties. labels May 23, 2026

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