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runtime: memory corruption from stack-allocated defer on 32-bit [1.14 backport] #41796

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gopherbot opened this issue Oct 5, 2020 · 3 comments
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@gopherbot
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@gopherbot gopherbot commented Oct 5, 2020

@aclements requested issue #41795 to be considered for backport to the next 1.14 minor release.

@gopherbot, please open backports to Go 1.15 and 1.14.

This can cause random memory corruption on 32-bit architectures. The circumstances for it happening are incredibly narrow, but the fix is also trivial.

@gopherbot
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@gopherbot gopherbot commented Oct 5, 2020

Change https://golang.org/cl/259597 mentions this issue: [release-branch.go1.14] runtime: correct signature of call16

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@dmitshur
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@dmitshur dmitshur commented Oct 8, 2020

Approving per discussion in a release meeting. This is a serious issue and the fix is trivial. This backport applies to both 1.15 (#41797) and 1.14 (this issue).

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@gopherbot
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@gopherbot gopherbot commented Oct 14, 2020

Closed by merging 0bf9410 to release-branch.go1.14.

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@gopherbot gopherbot closed this Oct 14, 2020
gopherbot pushed a commit that referenced this issue Oct 14, 2020
The signature of call16 is currently missing the "typ" parameter. This
CL fixes this. This wasn't caught by vet because call16 is defined by
macro expansion (see #17544), and we didn't notice the mismatch with
the other call* functions because call16 is defined only on 32-bit
architectures and lives alone in stubs32.go.

Unfortunately, this means its GC signature is also wrong: the "arg"
parameter is treated as a scalar rather than a pointer, so GC won't
trace it and stack copying won't adjust it. This turns out to matter
in exactly one case right now: on 32-bit architectures (which are the
only architectures where call16 is defined), a stack-allocated defer
of a function with a 16-byte or smaller argument frame including a
non-empty result area can corrupt memory if the deferred function
grows the stack and is invoked during a panic. Whew. All other current
uses of reflectcall pass a heap-allocated "arg" frame (which happens
to be reachable from other stack roots, so tracing isn't a problem).

Curiously, in 2016, the signatures of all call* functions were wrong
in exactly this way. CL 31654 fixed all of them in stubs.go, but
missed the one in stubs32.go.

Updates #41795.
Fixes #41796.

Change-Id: I31e3c0df201f79ee5707eeb8dc4ff0d13fc10ada
Reviewed-on: https://go-review.googlesource.com/c/go/+/259338
Trust: Austin Clements <austin@google.com>
Run-TryBot: Austin Clements <austin@google.com>
TryBot-Result: Go Bot <gobot@golang.org>
Reviewed-by: Cherry Zhang <cherryyz@google.com>
Reviewed-on: https://go-review.googlesource.com/c/go/+/259597
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