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| author | Roland Shoemaker <roland@golang.org> | 2026-02-24 08:58:39 -0800 |
|---|---|---|
| committer | Roland Shoemaker <roland@golang.org> | 2026-02-24 13:58:57 -0800 |
| commit | fa8595702eba16f757860705157f17f8054a92df (patch) | |
| tree | a77f444bced1cc293af91400d5ef542df28e4c93 /src/internal/runtime | |
| parent | e237976802f31e13e98cbde121fa0348f77d8df4 (diff) | |
| download | go-fa8595702eba16f757860705157f17f8054a92df.tar.xz | |
internal/runtime/sys: only use speculation barrier for DIT on Apple Silicon
The Apple documentation [0] indicates that when enabling DIT (via MSR),
a speculation barrier should be used. The rationale for this is not
explained, but one could assume that they perhaps do not treat MSR of
a PSTATE bit as a context synchronization event, and thus the CPU might
speculatively execute instructions that would be affected by DIT before
the MSR takes effect.
Arm on the other hand [1], explicitly states that MSR of a PSTATE bit is
a context synchronization event, and thus speculation barriers are not
needed.
In order to square this circle, we keep the speculation barrier, but
only use it on Apple Silicon.
[0] http://go/appledoc/xcode/writing-arm64-code-for-apple-platforms#Enable-DIT-for-constant-time-cryptographic-operations
[1] https://developer.arm.com/documentation/100941/0101/Barriers?lang=en
Fixes #77776
Change-Id: I17a91adc8e4d90fe2288592547986c82a9356cde
Reviewed-on: https://go-review.googlesource.com/c/go/+/748460
Reviewed-by: Keith Randall <khr@google.com>
Reviewed-by: Keith Randall <khr@golang.org>
LUCI-TryBot-Result: Go LUCI <golang-scoped@luci-project-accounts.iam.gserviceaccount.com>
Diffstat (limited to 'src/internal/runtime')
| -rw-r--r-- | src/internal/runtime/sys/dit_arm64.s | 8 |
1 files changed, 8 insertions, 0 deletions
diff --git a/src/internal/runtime/sys/dit_arm64.s b/src/internal/runtime/sys/dit_arm64.s index cc5642f838..483ac6bf21 100644 --- a/src/internal/runtime/sys/dit_arm64.s +++ b/src/internal/runtime/sys/dit_arm64.s @@ -11,9 +11,17 @@ TEXT ·EnableDIT(SB),$0-1 MOVB R1, ret+0(FP) TBNZ $0, R1, ret MSR $1, DIT +#ifdef GOOS_darwin + // Arm documents that barriers are not necessary when writing to, or reading + // from, PSTATE fields. However, Apple documentation indicates that barriers + // should be used, in particular when setting the PSTATE.DIT field. Barriers + // aren't cheap, so only use them on Apple silicon for now. + // + // See go.dev/issue/77776. MOVBU internal∕cpu·ARM64+const_offsetARM64HasSB(SB), R2 TBZ $0, R2, sbFallback SB +#endif ret: RET sbFallback: |