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loader, crypto/internal/entropy: fix 32 MiB RAM overflow on microcontrollers

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Go 1.26 added a CPU jitter-based SP 800-90B entropy source for FIPS 140-3
compliance (crypto/internal/entropy/v1.0.0). It declares a 32 MiB global
ScratchBuffer ([1<<25]byte) used for memory access timing noise. On systems
with virtual memory this stays in .noptrbss and is lazily paged, but on
baremetal targets it becomes static RAM, causing fatal overflow (e.g.
pybadge with 192 KB SRAM reports 33 MB overflow).

Since FIPS jitter entropy is never used on TinyGo targets (fips140.Enabled
is always false, so drbg.Read falls through to sysrand.Read), provide a
TinyGo overlay that replaces ScratchBuffer with [0]byte and stubs out all
entropy functions with panics.
This commit is contained in:
deadprogram
2026-04-10 13:38:36 +02:00
committed by Ron Evans
parent 3c07a36e95
commit c1f48fc79a
2 changed files with 66 additions and 0 deletions
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loader/goroot.go
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@@ -268,6 +268,16 @@ func pathsToOverride(goMinor int, needsSyscallPackage bool) map[string]bool {
paths["crypto/internal/boring/sig/"] = false
}
if goMinor >= 26 {
// Go 1.26 added a CPU jitter entropy source for FIPS 140-3 that
// allocates a 32 MiB global buffer (ScratchBuffer [1<<25]byte).
// This is fine on systems with virtual memory, but causes RAM
// overflow on microcontrollers. Replace with a zero-size stub
// since TinyGo targets never use FIPS jitter entropy.
paths["crypto/internal/entropy/"] = true
paths["crypto/internal/entropy/v1.0.0/"] = false
}
if needsSyscallPackage {
paths["syscall/"] = true // include syscall/js
paths["internal/syscall/"] = true