From 363b3fbfe3b5452a556047bd2c1e202b49d54ae9 Mon Sep 17 00:00:00 2001
From: Richard Zak <richard.j.zak@gmail.com>
Date: Sat, 9 Mar 2024 12:51:35 -0500
Subject: [PATCH] feat: use `libc::getauxval`

This is preferred as crt0stack::Reader::from_environ() relies on the
global environ pointer and:
1. The environ pointer is not guaranteed to point to memory before auxv
   by any standard I am aware of. It just happens to do so in some C
   library implementations if the environment has not been modified.
2. The environ pointer is definitely not going to point to memory before
   auxv after calling any environment modifying function such as
   setenv(3).

Calling getauxval(3) is the only standards compliant way of accessing
values in the auxiliary vector.

Co-authored-by: Patrick Oppenlander <patrick.oppenlander@gmail.com>
Signed-off-by: Richard Zak <richard.j.zak@gmail.com>
---
 Cargo.toml |  7 ++-----
 src/lib.rs | 14 +++++++-------
 2 files changed, 9 insertions(+), 12 deletions(-)

diff --git a/Cargo.toml b/Cargo.toml
index 1516939..73e7c05 100644
--- a/Cargo.toml
+++ b/Cargo.toml
@@ -11,7 +11,7 @@ description = "Resolve Linux vDSO symbols"
 readme = "README.md"
 keywords = ["linux", "vdso"]
 categories = ["development-tools", "os::linux-apis"]
-exclude = [ ".gitignore", ".github/*" ]
+exclude = [".gitignore", ".github/*"]
 
 # See more keys and their definitions at https://doc.rust-lang.org/cargo/reference/manifest.html
 
@@ -23,9 +23,6 @@ maintenance = { status = "actively-developed" }
 is-it-maintained-issue-resolution = { repository = "enarx/vdso" }
 is-it-maintained-open-issues = { repository = "enarx/vdso" }
 
-[dev-dependencies]
-libc = "0.2.67"
-
 [dependencies]
-crt0stack = "0.1"
 goblin = "0.8.0"
+libc = "0.2.153"
diff --git a/src/lib.rs b/src/lib.rs
index e62e256..0b6e4e2 100644
--- a/src/lib.rs
+++ b/src/lib.rs
@@ -5,7 +5,6 @@
 #![deny(missing_docs)]
 #![deny(clippy::all)]
 
-use crt0stack::{Entry, Reader};
 use std::ffi::CStr;
 use std::os::raw::c_char;
 use std::slice::from_raw_parts;
@@ -20,6 +19,7 @@ mod elf {
     pub use goblin::elf64::sym::Sym;
 
     pub const CLASS: u8 = ELFCLASS64;
+
     pub type Word = u64;
 }
 
@@ -33,6 +33,7 @@ mod elf {
     pub use goblin::elf32::sym::Sym;
 
     pub const CLASS: u8 = ELFCLASS32;
+
     pub type Word = u32;
 }
 
@@ -114,14 +115,13 @@ pub struct Vdso<'a>(&'a Header);
 impl Vdso<'static> {
     /// Locates the vDSO by parsing the auxiliary vectors
     pub fn locate() -> Option<Self> {
-        for aux in Reader::from_environ().done() {
-            if let Entry::SysInfoEHdr(addr) = aux {
-                let hdr = unsafe { Header::from_ptr(&*(addr as *const _))? };
-                return Some(Self(hdr));
-            }
+        let val = unsafe { libc::getauxval(libc::AT_SYSINFO_EHDR) };
+        if val == 0 {
+            return None;
         }
 
-        None
+        let hdr = unsafe { Header::from_ptr(&*(val as *const _))? };
+        Some(Self(hdr))
     }
 }