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std.debug: remove @frameAddress() "UAF"

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We can't call `@frameAddress()` and then immediately `return`! That
invalidates the frame. This *usually* isn't a problem, because the stack
walk `next` call will *probably* have a stack frame and it will
*probably* be at the exact same address, but neither of those is a
guarantee. On powerpc, presumably some unfortunate inlining was going
on, so this frame was indeed invalidated when we started walking frames.

We need to explicitly pass `@frameAddress` into any function which will
return before we actually walk the stack. Pretty simple patch.

Resolves: #24970
This commit is contained in:
mlugg 2025-08-27 21:35:45 +01:00 • committed by Matthew Lugg
parent 151c7dc74b
commit a31950aa57
2 changed files with 10 additions and 20 deletions
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28
lib/std/debug.zig
View file

@ -440,7 +440,7 @@ pub fn dumpStackTraceFromBase(context: *ThreadContext, stderr: *Writer) void {
return;
}
var it = StackIterator.initWithContext(null, debug_info, context) catch return;
var it = StackIterator.initWithContext(null, debug_info, context, @frameAddress()) catch return;
defer it.deinit();
// DWARF unwinding on aarch64-macos is not complete so we need to get pc address from mcontext
@ -499,12 +499,7 @@ pub fn captureStackTrace(first_address: ?usize, stack_trace: *std.builtin.StackT
// TODO: This should use the DWARF unwinder if .eh_frame_hdr is available (so that full debug info parsing isn't required).
// A new path for loading SelfInfo needs to be created which will only attempt to parse in-memory sections, because
// stopping to load other debug info (ie. source line info) from disk here is not required for unwinding.
if (builtin.cpu.arch == .powerpc64) {
// https://github.com/ziglang/zig/issues/24970
stack_trace.index = 0;
return;
}
var it = StackIterator.init(first_address, null);
var it = StackIterator.init(first_address, @frameAddress());
defer it.deinit();
for (stack_trace.instruction_addresses, 0..) |*addr, i| {
addr.* = it.next() orelse {
@ -787,7 +782,7 @@ pub const StackIterator = struct {
failed: bool = false,
} else void = if (have_ucontext) null else {},
pub fn init(first_address: ?usize, fp: ?usize) StackIterator {
pub fn init(first_address: ?usize, fp: usize) StackIterator {
if (native_arch.isSPARC()) {
// Flush all the register windows on stack.
asm volatile (if (builtin.cpu.has(.sparc, .v9))
@ -799,23 +794,18 @@ pub const StackIterator = struct {
return .{
.first_address = first_address,
// TODO: this is a workaround for #16876
//.fp = fp orelse @frameAddress(),
.fp = fp orelse blk: {
const fa = @frameAddress();
break :blk fa;
},
.fp = fp,
};
}
pub fn initWithContext(first_address: ?usize, debug_info: *SelfInfo, context: *posix.ucontext_t) !StackIterator {
pub fn initWithContext(first_address: ?usize, debug_info: *SelfInfo, context: *posix.ucontext_t, fp: usize) !StackIterator {
// The implementation of DWARF unwinding on aarch64-macos is not complete. However, Apple mandates that
// the frame pointer register is always used, so on this platform we can safely use the FP-based unwinder.
if (builtin.target.os.tag.isDarwin() and native_arch == .aarch64)
return init(first_address, @truncate(context.mcontext.ss.fp));
if (SelfInfo.supports_unwinding) {
var iterator = init(first_address, null);
var iterator = init(first_address, fp);
iterator.unwind_state = .{
.debug_info = debug_info,
.dwarf_context = try SelfInfo.UnwindContext.init(debug_info.allocator, context),
@ -823,7 +813,7 @@ pub const StackIterator = struct {
return iterator;
}
return init(first_address, null);
return init(first_address, fp);
}
pub fn deinit(it: *StackIterator) void {
@ -981,8 +971,8 @@ pub fn writeCurrentStackTrace(
const has_context = getContext(&context);
var it = (if (has_context) blk: {
break :blk StackIterator.initWithContext(start_addr, debug_info, &context) catch null;
} else null) orelse StackIterator.init(start_addr, null);
break :blk StackIterator.initWithContext(start_addr, debug_info, &context, @frameAddress()) catch null;
} else null) orelse StackIterator.init(start_addr, @frameAddress());
defer it.deinit();
while (it.next()) |return_address| {

2
test/standalone/stack_iterator/unwind.zig
View file

@ -10,7 +10,7 @@ noinline fn frame3(expected: *[4]usize, unwound: *[4]usize) void {
testing.expect(debug.getContext(&context)) catch @panic("failed to getContext");
const debug_info = debug.getSelfDebugInfo() catch @panic("failed to openSelfDebugInfo");
var it = debug.StackIterator.initWithContext(expected[0], debug_info, &context) catch @panic("failed to initWithContext");
var it = debug.StackIterator.initWithContext(expected[0], debug_info, &context, @frameAddress()) catch @panic("failed to initWithContext");
defer it.deinit();
for (unwound) |*addr| {