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cmd/link,debug/elf: mark Go binaries with no branch target CFI on openbsd

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OpenBSD enables Indirect Branch Tracking (IBT) on amd64 and Branch Target
Identification (BTI) on arm64, where hardware permits. Since Go generated
binaries do not currently support IBT or BTI, temporarily mark them with
PT_OPENBSD_NOBTCFI which prevents branch target CFI from being enforced
on execution. This should be removed as soon asn IBT and BTI support are
available.

Fixes #66040
Updates #66054

Change-Id: I91ac05736e6942c54502bef4b8815eb8740d2d5e
Reviewed-on: https://go-review.googlesource.com/c/go/+/568435
LUCI-TryBot-Result: Go LUCI <golang-scoped@luci-project-accounts.iam.gserviceaccount.com>
TryBot-Result: Gopher Robot <gobot@golang.org>
Reviewed-by: Josh Rickmar <jrick@zettaport.com>
Reviewed-by: Keith Randall <khr@golang.org>
Run-TryBot: Joel Sing <joel@sing.id.au>
Reviewed-by: Keith Randall <khr@google.com>
Reviewed-by: Than McIntosh <thanm@google.com>
This commit is contained in:
Joel Sing 2024-02-21 23:29:12 +11:00
parent 47d4295f92
commit 1e433915ce
5 changed files with 15 additions and 0 deletions
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2
api/next/66054.txt Normal file
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@ -0,0 +1,2 @@
pkg debug/elf, const PT_OPENBSD_NOBTCFI = 1705237480 #66054
pkg debug/elf, const PT_OPENBSD_NOBTCFI ProgType #66054

3
doc/next/6-stdlib/99-minor/debug/elf/66054.md Normal file
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@ -0,0 +1,3 @@
The debug/elf package now defines PT_OPENBSD_NOBTCFI. This elf.ProgType is
used to disable Branch Tracking Control Flow Integrity (BTCFI) enforcement
on OpenBSD binaries.

4
src/cmd/link/internal/ld/elf.go
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@ -2185,6 +2185,10 @@ func asmbElf(ctxt *Link) {
ph.Type = elf.PT_GNU_STACK
ph.Flags = elf.PF_W + elf.PF_R
ph.Align = uint64(ctxt.Arch.RegSize)
} else if ctxt.HeadType == objabi.Hopenbsd {
ph := newElfPhdr()
ph.Type = elf.PT_OPENBSD_NOBTCFI
ph.Flags = elf.PF_X
} else if ctxt.HeadType == objabi.Hsolaris {
ph := newElfPhdr()
ph.Type = elf.PT_SUNWSTACK

5
src/cmd/link/internal/ld/lib.go
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@ -1437,6 +1437,11 @@ func (ctxt *Link) hostlink() {
}
case objabi.Hopenbsd:
argv = append(argv, "-Wl,-nopie")
if linkerFlagSupported(ctxt.Arch, argv[0], "", "-Wl,-z,nobtcfi") {
// -Wl,-z,nobtcfi is only supported on OpenBSD 7.4+, remove guard
// when OpenBSD 7.5 is released and 7.3 is no longer supported.
argv = append(argv, "-Wl,-z,nobtcfi")
}
argv = append(argv, "-pthread")
if ctxt.Arch.InFamily(sys.ARM64) {
// Disable execute-only on openbsd/arm64 - the Go arm64 assembler

1
src/debug/elf/elf.go
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@ -773,6 +773,7 @@ const (
PT_OPENBSD_RANDOMIZE ProgType = 0x65a3dbe6 /* Random data */
PT_OPENBSD_WXNEEDED ProgType = 0x65a3dbe7 /* W^X violations */
PT_OPENBSD_NOBTCFI ProgType = 0x65a3dbe8 /* No branch target CFI */
PT_OPENBSD_BOOTDATA ProgType = 0x65a41be6 /* Boot arguments */
PT_SUNW_EH_FRAME ProgType = 0x6474e550 /* Frame unwind information */