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cmd/asm, cmd/compile, runtime: add -spectre=ret mode

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This commit extends the -spectre flag to cmd/asm and adds
a new Spectre mitigation mode "ret", which enables the use
of retpolines.

Retpolines prevent speculation about the target of an indirect
jump or call and are described in more detail here:
https://support.google.com/faqs/answer/7625886

Change-Id: I4f2cb982fa94e44d91e49bd98974fd125619c93a
Reviewed-on: https://go-review.googlesource.com/c/go/+/222661
Reviewed-by: Keith Randall <khr@golang.org>
This commit is contained in:
Russ Cox 2020-01-17 13:54:30 -05:00
parent 877ef86bec
commit fc8a6336d1
13 changed files with 119 additions and 1 deletions
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13
src/cmd/asm/main.go
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@ -41,6 +41,19 @@ func main() {
ctxt.Flag_dynlink = *flags.Dynlink
ctxt.Flag_shared = *flags.Shared || *flags.Dynlink
ctxt.Flag_newobj = *flags.Newobj
switch *flags.Spectre {
default:
log.Printf("unknown setting -spectre=%s", *flags.Spectre)
os.Exit(2)
case "":
// nothing
case "index":
// known to compiler; ignore here so people can use
// the same list with -gcflags=-spectre=LIST and -asmflags=-spectrre=LIST
case "all", "ret":
ctxt.Retpoline = true
}
ctxt.Bso = bufio.NewWriter(os.Stdout)
defer ctxt.Bso.Flush()