runtime: msanwrite segfaults when called without a g on arm64

[zhangfannie]

What version of Go are you using (go version)?

$ go version
go version devel +c3c53661ba Tue Sep 17 04:37:46 2019 +0000 linux/arm64

Does this issue reproduce with the latest release?

yes

What operating system and processor architecture are you using (go env)?

go env Output

$ go env
GO111MODULE=""
GOARCH="arm64"
GOBIN=""
GOCACHE="/home/fanzha02/.cache/go-build"
GOENV="/home/fanzha02/.config/go/env"
GOEXE=""
GOFLAGS=""
GOHOSTARCH="arm64"
GOHOSTOS="linux"
GONOPROXY=""
GONOSUMDB=""
GOOS="linux"
GOPATH="/home/fanzha02/go"
GOPRIVATE=""
GOPROXY="https://proxy.golang.org,direct"
GOROOT="/home/fanzha02/work/go_project/gomain"
GOSUMDB="sum.golang.org"
GOTMPDIR=""
GOTOOLDIR="/home/fanzha02/work/go_project/gomain/pkg/tool/linux_arm64"
GCCGO="gccgo"
AR="ar"
CC="gcc"
CXX="g++"
CGO_ENABLED="1"
GOMOD="/home/fanzha02/work/go_project/gomain/src/go.mod"
CGO_CFLAGS="-g -O2"
CGO_CPPFLAGS=""
CGO_CXXFLAGS="-g -O2"
CGO_FFLAGS="-g -O2"
CGO_LDFLAGS="-g -O2"
PKG_CONFIG="pkg-config"
GOGCCFLAGS="-fPIC -pthread -fmessage-length=0 -fdebug-prefix-map=/tmp/go-build714027259=/tmp/go-build -gno-record-gcc-switches"

What did you do?

Run testsanitizers/TestShared test

cd $GOROOT/src
run the command: CC=clang ../bin/go tool dist test -run testsanitizers
clang version: clang --version
clang version 6.0.0-1ubuntu2 (tags/RELEASE_600/final)
Target: aarch64-unknown-linux-gnu
Thread model: posix
InstalledDir: /usr/bin

What did you expect to see?

pass

What did you see instead?

The test failed.

../misc/cgo/testsanitizers

--- FAIL: TestShared (0.24s)
--- FAIL: TestShared/msan_shared (4.69s)
cshared_test.go:71: /tmp/TestShared066999108/msan_shared exited with exit status 77
MemorySanitizer:DEADLYSIGNAL
==24668==ERROR: MemorySanitizer: SEGV on unknown address 0x000000000030 (pc 0xffff94b3e9d4 bp 0xffffef3ca388 sp 0xffffef3ca390 T24668)
==24668==The signal is caused by a READ memory access.
==24668==Hint: address points to the zero page.
#0 0xffff94b3e9d3 (/tmp/TestShared066999108/libmsan_shared.so+0x8e9d3)

        MemorySanitizer can not provide additional info.
        SUMMARY: MemorySanitizer: SEGV (/tmp/TestShared066999108/libmsan_shared.so+0x8e9d3)
        ==24668==ABORTING

FAIL

[zhangfannie]

The cause is that when built with -buildmode=c-shared, the sigaction() of runtime/cgo_sigaction.go will call msanwrite() during libpreinit (before the runtime has set up a g). Unfortunately, on arm64, msancall() called by msanwrite() assumes that it is always called with a valid g, leading to a segfault.

I will submit the fixed CL, checking for nil g in msancall() on arm64.

[toothrot]

/cc @bcmills and @ianlancetaylor who know much more about runtime/cgo than myself.

[ianlancetaylor]

The suggested change sounds correct. That is what the amd64 code already does.

[ianlancetaylor]

The change should be to msancall<> in runtime/msan_arm64.s.

[zhangfannie]

@ianlancetaylor Yes, you are right. We need to check nil g to msancall() in runtime/msan_arm64.s. The fixed patch is ready and I will submit it. Thank you.

[gopherbot]

Change https://golang.org/cl/196157 mentions this issue: runtime: check for nil g in msancall() on arm64