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linux: do not set stack size hard limit

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At main startup, if the ELF auxiliary vector contains a stacksize value,
use it as a hint for the minimum stacksize required by the executable.

1. Never lower the hard-limit. Once a hard-limit is lowered, then it can
   never be increased (including child processes).

2. If hint exceeds hard-limit then clamp hint to hard-limit.

3. If soft-limit exceeds hint then do nothing.
This commit is contained in:
Michael Dusan 2023-07-25 21:44:11 -04:00 committed by Andrew Kelley
parent e66190025f
commit 2dd7c6b268
1 changed files with 22 additions and 15 deletions
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37
lib/std/start.zig
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@ -459,22 +459,29 @@ fn expandStackSize(phdrs: []elf.Phdr) void {
for (phdrs) |*phdr| {
switch (phdr.p_type) {
elf.PT_GNU_STACK => {
const wanted_stack_size = phdr.p_memsz;
assert(wanted_stack_size % std.mem.page_size == 0);
assert(phdr.p_memsz % std.mem.page_size == 0);
std.os.setrlimit(.STACK, .{
.cur = wanted_stack_size,
.max = wanted_stack_size,
}) catch {
// Because we could not increase the stack size to the upper bound,
// depending on what happens at runtime, a stack overflow may occur.
// However it would cause a segmentation fault, thanks to stack probing,
// so we do not have a memory safety issue here.
// This is intentional silent failure.
// This logic should be revisited when the following issues are addressed:
// https://github.com/ziglang/zig/issues/157
// https://github.com/ziglang/zig/issues/1006
};
// Silently fail if we are unable to get limits.
const limits = std.os.getrlimit(.STACK) catch break;
// Clamp to limits.max .
const wanted_stack_size = @min(phdr.p_memsz, limits.max);
if (wanted_stack_size > limits.cur) {
std.os.setrlimit(.STACK, .{
.cur = wanted_stack_size,
.max = limits.max,
}) catch {
// Because we could not increase the stack size to the upper bound,
// depending on what happens at runtime, a stack overflow may occur.
// However it would cause a segmentation fault, thanks to stack probing,
// so we do not have a memory safety issue here.
// This is intentional silent failure.
// This logic should be revisited when the following issues are addressed:
// https://github.com/ziglang/zig/issues/157
// https://github.com/ziglang/zig/issues/1006
};
}
break;
},
else => {},