[release-branch.go1.16] misc/wasm, cmd/link: do not let command line args overwrite...

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 <cherryyz@google.com>.

For #48797
Fixes #48799
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 <bracewell@google.com>
Reviewed-by: Than McIntosh <thanm@google.com>
Reviewed-on: https://go-review.googlesource.com/c/go/+/354591
Trust: Michael Knyszek <mknyszek@google.com>
Reviewed-by: Heschi Kreinick <heschi@google.com>

diff --git a/misc/wasm/wasm_exec.js b/misc/wasm/wasm_exec.js
index 82041e6bb901bde57c43e689984e60a499573aca..a0a264278b1b1d2a7e7232d111a3009241a01f77 100644 (file)
--- a/misc/wasm/wasm_exec.js
+++ b/misc/wasm/wasm_exec.js
@@ -564,6 +564,13 @@
                                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 52035e96301cf4639ede631b6ce4d4a2f907108f..54a1d188cdb955d8e35c3d9ce009424e7cd4907a 100644 (file)
--- a/src/cmd/link/internal/ld/data.go
+++ b/src/cmd/link/internal/ld/data.go
@@ -2330,6 +2330,11 @@ func assignAddress(ctxt *Link, sect *sym.Section, n int, s loader.Sym, va uint64
        return sect, n, va
 }
 
+// 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 {
@@ -2339,10 +2344,14 @@ 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)