From 4925e0766f8a92ab82913b3564228645613290f5 Mon Sep 17 00:00:00 2001 From: Michael Knyszek Date: Thu, 2 Sep 2021 16:51:59 -0400 Subject: [release-branch.go1.17] misc/wasm, cmd/link: do not let command line args overwrite global data On Wasm, wasm_exec.js puts command line arguments at the beginning of the linear memory (following the "zero page"). Currently there is no limit for this, and a very long command line can overwrite the program's data section. Prevent this by limiting the command line to 4096 bytes, and in the linker ensuring the data section starts at a high enough address (8192). (Arguably our address assignment on Wasm is a bit confusing. This is the minimum fix I can come up with.) Thanks to Ben Lubar for reporting this issue. Change by Cherry Mui . For #48797 Fixes #48800 Fixes CVE-2021-38297 Change-Id: I0f50fbb2a5b6d0d047e3c134a88988d9133e4ab3 Reviewed-on: https://team-review.git.corp.google.com/c/golang/go-private/+/1205933 Reviewed-by: Roland Shoemaker Reviewed-by: Than McIntosh Reviewed-on: https://go-review.googlesource.com/c/go/+/354592 Trust: Michael Knyszek Reviewed-by: Heschi Kreinick --- misc/wasm/wasm_exec.js | 7 +++++++ src/cmd/link/internal/ld/data.go | 11 ++++++++++- 2 files changed, 17 insertions(+), 1 deletion(-) diff --git a/misc/wasm/wasm_exec.js b/misc/wasm/wasm_exec.js index 231185a123e..df7a6b848f9 100644 --- a/misc/wasm/wasm_exec.js +++ b/misc/wasm/wasm_exec.js @@ -567,6 +567,13 @@ offset += 8; }); + // The linker guarantees global data starts from at least wasmMinDataAddr. + // Keep in sync with cmd/link/internal/ld/data.go:wasmMinDataAddr. + const wasmMinDataAddr = 4096 + 4096; + if (offset >= wasmMinDataAddr) { + throw new Error("command line too long"); + } + this._inst.exports.run(argc, argv); if (this.exited) { this._resolveExitPromise(); diff --git a/src/cmd/link/internal/ld/data.go b/src/cmd/link/internal/ld/data.go index 70fbb9dc4e2..9abf761038c 100644 --- a/src/cmd/link/internal/ld/data.go +++ b/src/cmd/link/internal/ld/data.go @@ -2450,6 +2450,11 @@ func splitTextSections(ctxt *Link) bool { return (ctxt.IsPPC64() || (ctxt.IsARM64() && ctxt.IsDarwin())) && ctxt.IsExternal() } +// On Wasm, we reserve 4096 bytes for zero page, then 4096 bytes for wasm_exec.js +// to store command line args. Data sections starts from at least address 8192. +// Keep in sync with wasm_exec.js. +const wasmMinDataAddr = 4096 + 4096 + // address assigns virtual addresses to all segments and sections and // returns all segments in file order. func (ctxt *Link) address() []*sym.Segment { @@ -2459,10 +2464,14 @@ func (ctxt *Link) address() []*sym.Segment { order = append(order, &Segtext) Segtext.Rwx = 05 Segtext.Vaddr = va - for _, s := range Segtext.Sections { + for i, s := range Segtext.Sections { va = uint64(Rnd(int64(va), int64(s.Align))) s.Vaddr = va va += s.Length + + if ctxt.IsWasm() && i == 0 && va < wasmMinDataAddr { + va = wasmMinDataAddr + } } Segtext.Length = va - uint64(*FlagTextAddr) -- cgit v1.2.3-54-g00ecf