Rollup merge of #68824 - ajpaverd:cfguard-rustbuild, r=Mark-Simulacrum

Enable Control Flow Guard in rustbuild

Now that Rust supports Control Flow Guard (#68180), add a config.toml option to build the standard library with CFG enabled.

r? @nagisa

1 files changed, 34 insertions, 0 deletions

diff --git a/src/doc/unstable-book/src/compiler-flags/control-flow-guard.md b/src/doc/unstable-book/src/compiler-flags/control-flow-guard.md
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+# `control_flow_guard`
+
+The tracking issue for this feature is: [#68793](https://github.com/rust-lang/rust/issues/68793).
+
+------------------------
+
+The `-Zcontrol_flow_guard=checks` compiler flag enables the Windows [Control Flow Guard][cfguard-docs] platform security feature. When enabled, the compiler outputs a list of valid indirect call targets, and inserts runtime checks on all indirect jump instructions to ensure that the destination is in the list of valid call targets.
+
+[cfguard-docs]: https://docs.microsoft.com/en-us/windows/win32/secbp/control-flow-guard
+
+For testing purposes, the `-Zcontrol_flow_guard=nochecks` compiler flag can be used to emit only the list of valid call targets, but not the runtime checks.
+
+It is strongly recommended to also enable Control Flow Guard checks in all linked libraries, including the standard library. 
+
+To enable Control Flow Guard in the standard library, you can use the [cargo `-Zbuild-std` functionality][build-std] to recompile the standard library with the same configuration options as the main program. 
+
+[build-std]: https://doc.rust-lang.org/nightly/cargo/reference/unstable.html#build-std
+
+For example:
+```cmd
+rustup toolchain install --force nightly
+rustup component add rust-src
+SET RUSTFLAGS=-Zcontrol_flow_guard=checks
+cargo +nightly build -Z build-std --target x86_64-pc-windows-msvc
+```
+
+```PowerShell
+rustup toolchain install --force nightly
+rustup component add rust-src
+$Env:RUSTFLAGS = "-Zcontrol_flow_guard=checks"
+cargo +nightly build -Z build-std --target x86_64-pc-windows-msvc
+```
+
+Alternatively, if you are building the standard library from source, you can set `control-flow-guard = true` in the config.toml file.