From 6d132345ee2eb2f780702a2ff7b3e5ee53840fb6 Mon Sep 17 00:00:00 2001
From: 4lDO2 <4lDO2@protonmail.com>
Date: Sun, 2 Jan 2022 11:57:34 +0100
Subject: [PATCH] WIP: Replace fexec with exec.

---
 src/call.rs   | 17 +++++++++++++----
 src/data.rs   | 30 ++++++++++++++++++++++++++++++
 src/number.rs |  2 +-
 3 files changed, 44 insertions(+), 5 deletions(-)

diff --git a/src/call.rs b/src/call.rs
index f6eb89c..8cf2876 100644
--- a/src/call.rs
+++ b/src/call.rs
@@ -1,5 +1,5 @@
 use super::arch::*;
-use super::data::{Map, SigAction, Stat, StatVfs, TimeSpec};
+use super::data::{ExecMemRange, Map, SigAction, Stat, StatVfs, TimeSpec};
 use super::error::Result;
 use super::flag::*;
 use super::number::*;
@@ -85,9 +85,18 @@ pub fn fcntl(fd: usize, cmd: usize, arg: usize) -> Result<usize> {
     unsafe { syscall3(SYS_FCNTL, fd, cmd, arg) }
 }
 
-/// Replace the current process with a new executable
-pub fn fexec(fd: usize, args: &[[usize; 2]], vars: &[[usize; 2]]) -> Result<usize> {
-    unsafe { syscall5(SYS_FEXEC, fd, args.as_ptr() as usize, args.len(), vars.as_ptr() as usize, vars.len()) }
+// TODO: Support specifying FDs to keep/close (for FDs not included in that list, it would take
+// into account O_CLOEXEC).
+// TODO: Allow setting all registers of the target process?
+/// Replace the current process with a new executable, allowing the user to specify memory ranges
+/// to either keep, move, or add. It will then jump to [`instruction_ptr`] in the new process
+/// memory specified by the range map, with the stack pointer set accordingly. This syscall does
+/// not support setuid/setgid; instead, privilege escalation must be done by a higher-privileged
+/// process performing these actions via ptrace.
+// TODO: never type
+pub fn exec(memranges: &[ExecMemRange], instruction_ptr: usize, stack_ptr: usize) -> Result<core::convert::Infallible> {
+    unsafe { syscall4(SYS_EXEC, memranges.as_ptr() as usize, memranges.len(), instruction_ptr, stack_ptr)?; }
+    panic!("SYS_EXEC should only return in case of an error");
 }
 
 /// Map a file into memory, but with the ability to set the address to map into, either as a hint
diff --git a/src/data.rs b/src/data.rs
index 45d2dd8..efd1bc2 100644
--- a/src/data.rs
+++ b/src/data.rs
@@ -295,3 +295,33 @@ macro_rules! ptrace_event {
         }
     }
 }
+
+#[repr(C)]
+pub struct ExecMemRange {
+    /// The address where the range is intended to be.
+    pub address: usize,
+    /// The size of the memory range.
+    pub size: usize,
+    /// Flags describing permissions (i.e. R/W/X)
+    pub flags: MapFlags,
+    /// If this equals [`address`], the range is kept untouched although flags can change, and the
+    /// range can be shortened or partly zeroed. If it is different, it will move `[old_address,
+    /// old_address+size)` to `[address, address+size]`.
+    pub old_address: usize,
+}
+impl Deref for ExecMemRange {
+    type Target = [u8];
+    fn deref(&self) -> &[u8] {
+        unsafe {
+            slice::from_raw_parts(self as *const ExecMemRange as *const u8, mem::size_of::<ExecMemRange>())
+        }
+    }
+}
+
+impl DerefMut for ExecMemRange {
+    fn deref_mut(&mut self) -> &mut [u8] {
+        unsafe {
+            slice::from_raw_parts_mut(self as *mut ExecMemRange as *mut u8, mem::size_of::<ExecMemRange>())
+        }
+    }
+}
diff --git a/src/number.rs b/src/number.rs
index 1f037eb..1d6f17b 100644
--- a/src/number.rs
+++ b/src/number.rs
@@ -26,7 +26,6 @@ pub const SYS_FCHMOD: usize =     SYS_CLASS_FILE | 94;
 pub const SYS_FCHOWN: usize =     SYS_CLASS_FILE | 207;
 pub const SYS_FCNTL: usize =      SYS_CLASS_FILE | 55;
 pub const SYS_FEVENT: usize =     SYS_CLASS_FILE | 927;
-pub const SYS_FEXEC: usize =      SYS_CLASS_FILE | 11;
 pub const SYS_FMAP_OLD: usize =   SYS_CLASS_FILE | SYS_ARG_SLICE | 90;
 pub const SYS_FMAP: usize =       SYS_CLASS_FILE | SYS_ARG_SLICE | 900;
 pub const SYS_FUNMAP_OLD: usize = SYS_CLASS_FILE | 91;
@@ -39,6 +38,7 @@ pub const SYS_FSYNC: usize =      SYS_CLASS_FILE | 118;
 pub const SYS_FTRUNCATE: usize =  SYS_CLASS_FILE | 93;
 pub const SYS_FUTIMENS: usize =   SYS_CLASS_FILE | SYS_ARG_SLICE | 320;
 
+pub const SYS_EXEC: usize =     101;
 pub const SYS_CHDIR: usize =    12;
 pub const SYS_CLOCK_GETTIME: usize = 265;
 pub const SYS_CLONE: usize =    120;