From 1fe0a138f97bc5dc59deb23e7c55fa628035996a Mon Sep 17 00:00:00 2001
From: Zhang Junyang <junyang@stu.pku.edu.cn>
Date: Wed, 16 Oct 2024 18:07:01 +0800
Subject: [PATCH] `PROT_WRITE` implies `PROT_READ` on x86

---
 kernel/src/syscall/mmap.rs     |  9 +++++++++
 kernel/src/syscall/mprotect.rs | 10 ++++++++++
 2 files changed, 19 insertions(+)

diff --git a/kernel/src/syscall/mmap.rs b/kernel/src/syscall/mmap.rs
index 948014f9b..93bc277ab 100644
--- a/kernel/src/syscall/mmap.rs
+++ b/kernel/src/syscall/mmap.rs
@@ -74,6 +74,15 @@ fn do_sys_mmap(
         return_errno_with_message!(Errno::ENOMEM, "mmap (addr + len) too large");
     }
 
+    // On x86, `PROT_WRITE` implies `PROT_READ`.
+    // <https://man7.org/linux/man-pages/man2/mmap.2.html>
+    #[cfg(target_arch = "x86_64")]
+    let vm_perms = if !vm_perms.contains(VmPerms::READ) && vm_perms.contains(VmPerms::WRITE) {
+        vm_perms | VmPerms::READ
+    } else {
+        vm_perms
+    };
+
     let root_vmar = ctx.process.root_vmar();
     let vm_map_options = {
         let mut options = root_vmar.new_map(len, vm_perms)?;
diff --git a/kernel/src/syscall/mprotect.rs b/kernel/src/syscall/mprotect.rs
index 62fd7c8c5..f55c5f8dc 100644
--- a/kernel/src/syscall/mprotect.rs
+++ b/kernel/src/syscall/mprotect.rs
@@ -32,6 +32,16 @@ pub fn sys_mprotect(addr: Vaddr, len: usize, perms: u64, ctx: &Context) -> Resul
         "integer overflow when (addr + len)",
     ))?;
     let range = addr..end;
+
+    // On x86, `PROT_WRITE` implies `PROT_READ`.
+    // <https://man7.org/linux/man-pages/man2/mprotect.2.html>
+    #[cfg(target_arch = "x86_64")]
+    let vm_perms = if !vm_perms.contains(VmPerms::READ) && vm_perms.contains(VmPerms::WRITE) {
+        vm_perms | VmPerms::READ
+    } else {
+        vm_perms
+    };
+
     root_vmar.protect(vm_perms, range)?;
     Ok(SyscallReturn::Return(0))
 }