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Adjust frame IP in backtraces relative to image base for SGX target #117895

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merged 3 commits into from
Nov 19, 2023
Merged

Adjust frame IP in backtraces relative to image base for SGX target #117895

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6e7ea03
Adjust frame IP in backtraces relative to image base for SGX target
mzohreva Nov 14, 2023
ec8c3d9
Move SGX-specific image base logic to sys_common
mzohreva Nov 14, 2023
b576dd2
Use ptr::invalid_mut for SGX image base
mzohreva Nov 17, 2023
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3 changes: 2 additions & 1 deletion library/std/src/backtrace.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -95,7 +95,7 @@ use crate::fmt;
use crate::panic::UnwindSafe;
use crate::sync::atomic::{AtomicUsize, Ordering::Relaxed};
use crate::sync::LazyLock;
use crate::sys_common::backtrace::{lock, output_filename};
use crate::sys_common::backtrace::{lock, output_filename, set_image_base};
use crate::vec::Vec;

/// A captured OS thread stack backtrace.
Expand Down Expand Up @@ -327,6 +327,7 @@ impl Backtrace {
let _lock = lock();
let mut frames = Vec::new();
let mut actual_start = None;
set_image_base();
unsafe {
backtrace_rs::trace_unsynchronized(|frame| {
frames.push(BacktraceFrame {
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12 changes: 12 additions & 0 deletions library/std/src/sys_common/backtrace.rs
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Expand Up @@ -64,6 +64,7 @@ unsafe fn _print_fmt(fmt: &mut fmt::Formatter<'_>, print_fmt: PrintFmt) -> fmt::
let mut first_omit = true;
// Start immediately if we're not using a short backtrace.
let mut start = print_fmt != PrintFmt::Short;
set_image_base();
backtrace_rs::trace_unsynchronized(|frame| {
if print_fmt == PrintFmt::Short && idx > MAX_NB_FRAMES {
return false;
Expand Down Expand Up @@ -213,3 +214,14 @@ pub fn output_filename(
}
fmt::Display::fmt(&file.display(), fmt)
}

#[cfg(all(target_vendor = "fortanix", target_env = "sgx"))]
pub fn set_image_base() {
let image_base = crate::os::fortanix_sgx::mem::image_base();
backtrace_rs::set_image_base(crate::ptr::from_exposed_addr_mut(image_base as _));
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Is this API implying that the backtrace generation is going to do more than math with the pointer value here? i.e., read/write from it? It seems odd to me to call from_exposed_addr here, vs. invalid_mut, which feels like it more appropriately describes the opaque nature of this pointer and theoretically hints that no one should read from it.

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No, backtrace is only using this for adjusting frame IPs. Having read the docs in https://doc.rust-lang.org/nightly/std/ptr/index.html I was under the impression that doing pointer arithmetic also requires strict provenance.

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See https://github.com/rust-lang/backtrace-rs/blob/master/src/backtrace/libunwind.rs#L38-L55

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I would not expect arithmetic with non-unsafe functions to ever require provenance. It looks like that code is operating on usize even, so it's not even doing pointer arithmetic I think.

}

#[cfg(not(all(target_vendor = "fortanix", target_env = "sgx")))]
pub fn set_image_base() {
// nothing to do for platforms other than SGX
}