mmap/munmap/mremamp shims

src/concurrency/data_race.rs

@@ -697,7 +697,8 @@ impl VClockAlloc {
                 MiriMemoryKind::Rust
                 | MiriMemoryKind::Miri
                 | MiriMemoryKind::C
-                | MiriMemoryKind::WinHeap,
+                | MiriMemoryKind::WinHeap
+                | MiriMemoryKind::Mmap,
             )
             | MemoryKind::Stack => {
                 let (alloc_index, clocks) = global.current_thread_state(thread_mgr);

src/machine.rs

@@ -104,6 +104,8 @@ pub enum MiriMemoryKind {
     /// Memory for thread-local statics.
     /// This memory may leak.
     Tls,
+    /// Memory mapped directly by the program
+    Mmap,
 }
 
 impl From<MiriMemoryKind> for MemoryKind<MiriMemoryKind> {
@@ -119,7 +121,7 @@ impl MayLeak for MiriMemoryKind {
         use self::MiriMemoryKind::*;
         match self {
             Rust | Miri | C | WinHeap | Runtime => false,
-            Machine | Global | ExternStatic | Tls => true,
+            Machine | Global | ExternStatic | Tls | Mmap => true,
         }
     }
 }
@@ -137,6 +139,7 @@ impl fmt::Display for MiriMemoryKind {
             Global => write!(f, "global (static or const)"),
             ExternStatic => write!(f, "extern static"),
             Tls => write!(f, "thread-local static"),
+            Mmap => write!(f, "mmap"),
         }
     }
 }
@@ -674,6 +677,15 @@ impl<'mir, 'tcx> MiriMachine<'mir, 'tcx> {
         let def_id = frame.instance.def_id();
         def_id.is_local() || self.local_crates.contains(&def_id.krate)
     }
+
+    pub(crate) fn round_up_to_multiple_of_page_size(&self, length: u64) -> Option<u64> {
+        #[allow(clippy::integer_arithmetic)] // page size is nonzero
+        (length.checked_add(self.page_size - 1)? / self.page_size).checked_mul(self.page_size)
+    }
+
+    pub(crate) fn page_align(&self) -> Align {
+        Align::from_bytes(self.page_size).unwrap()
+    }
 }
 
 impl VisitTags for MiriMachine<'_, '_> {

src/shims/unix/foreign_items.rs

@@ -10,6 +10,7 @@ use rustc_target::spec::abi::Abi;
 use crate::*;
 use shims::foreign_items::EmulateByNameResult;
 use shims::unix::fs::EvalContextExt as _;
+use shims::unix::mem::EvalContextExt as _;
 use shims::unix::sync::EvalContextExt as _;
 use shims::unix::thread::EvalContextExt as _;
 
@@ -213,6 +214,22 @@ pub trait EvalContextExt<'mir, 'tcx: 'mir>: crate::MiriInterpCxExt<'mir, 'tcx> {
                 }
             }
 
+            "mmap" => {
+                let [addr, length, prot, flags, fd, offset] = this.check_shim(abi, Abi::C {unwind: false}, link_name, args)?;
+                let ptr = this.mmap(addr, length, prot, flags, fd, offset)?;
+                this.write_scalar(ptr, dest)?;
+            }
+            "mremap" => {
+                let [old_address, old_size, new_size, flags] = this.check_shim(abi, Abi::C {unwind: false}, link_name, args)?;
+                let ptr = this.mremap(old_address, old_size, new_size, flags)?;
+                this.write_scalar(ptr, dest)?;
+            }
+            "munmap" => {
+                let [addr, length] = this.check_shim(abi, Abi::C {unwind: false}, link_name, args)?;
+                let result = this.munmap(addr, length)?;
+                this.write_scalar(result, dest)?;
+            }
+
             // Dynamic symbol loading
             "dlsym" => {
                 let [handle, symbol] = this.check_shim(abi, Abi::C { unwind: false }, link_name, args)?;

src/shims/unix/macos/foreign_items.rs

@@ -197,16 +197,6 @@ pub trait EvalContextExt<'mir, 'tcx: 'mir>: crate::MiriInterpCxExt<'mir, 'tcx> {
                 this.write_scalar(res, dest)?;
             }
 
-            // Incomplete shims that we "stub out" just to get pre-main initialization code to work.
-            // These shims are enabled only when the caller is in the standard library.
-            "mmap" if this.frame_in_std() => {
-                // This is a horrible hack, but since the guard page mechanism calls mmap and expects a particular return value, we just give it that value.
-                let [addr, _, _, _, _, _] =
-                    this.check_shim(abi, Abi::C { unwind: false }, link_name, args)?;
-                let addr = this.read_scalar(addr)?;
-                this.write_scalar(addr, dest)?;
-            }
-
             _ => return Ok(EmulateByNameResult::NotSupported),
         };
 

src/shims/unix/mem.rs

@@ -0,0 +1,207 @@
+//! This is an incomplete implementation of mmap/mremap/munmap which is restricted in order to be
+//! implementable on top of the existing memory system. The point of these function as-written is
+//! to allow memory allocators written entirely in Rust to be executed by Miri. This implementation
+//! does not support other uses of mmap such as file mappings.
+//!
+//! mmap/mremap/munmap behave a lot like alloc/realloc/dealloc, and for simple use they are exactly
+//! equivalent. But the memory-mapping API provides more control. For example:
+//!
+//! * It is possible to munmap a single page in the middle of a mapped region. We do not have a way
+//! to express non-contiguous allocations.
+//!
+//! * With MAP_FIXED it is possible to call mmap multiple times, but create a single contiguous
+//! range of mapped virtual addresses. A memory allocator can then choose to carve this up into
+//! allocations in arbitrary ways.
+
+use crate::*;
+use rustc_target::abi::{Align, Size};
+
+impl<'mir, 'tcx: 'mir> EvalContextExt<'mir, 'tcx> for crate::MiriInterpCx<'mir, 'tcx> {}
+pub trait EvalContextExt<'mir, 'tcx: 'mir>: crate::MiriInterpCxExt<'mir, 'tcx> {
+    fn mmap(
+        &mut self,
+        addr: &OpTy<'tcx, Provenance>,
+        length: &OpTy<'tcx, Provenance>,
+        prot: &OpTy<'tcx, Provenance>,
+        flags: &OpTy<'tcx, Provenance>,
+        fd: &OpTy<'tcx, Provenance>,
+        offset: &OpTy<'tcx, Provenance>,
+    ) -> InterpResult<'tcx, Scalar<Provenance>> {
+        let this = self.eval_context_mut();
+
+        // We do not support MAP_FIXED, so the addr argument is always ignored
+        let addr = this.read_pointer(addr)?;
+        let length = this.read_scalar(length)?.to_machine_usize(this)?;
+        let prot = this.read_scalar(prot)?.to_i32()?;
+        let flags = this.read_scalar(flags)?.to_i32()?;
+        let fd = this.read_scalar(fd)?.to_i32()?;
+        let offset = this.read_scalar(offset)?.to_machine_usize(this)?;
+
+        let map_private = this.eval_libc_i32("MAP_PRIVATE");
+        let map_anonymous = this.eval_libc_i32("MAP_ANONYMOUS");
+        let map_shared = this.eval_libc_i32("MAP_SHARED");
+        let map_fixed = this.eval_libc_i32("MAP_FIXED");
+
+        // This is a horrible hack, but since the guard page mechanism calls mmap and expects a particular return value, we just give it that value.
+        if this.frame_in_std() && this.tcx.sess.target.os == "macos" && (flags & map_fixed) != 0 {
+            return Ok(Scalar::from_maybe_pointer(addr, this));
+        }
+
+        let prot_read = this.eval_libc_i32("PROT_READ");
+        let prot_write = this.eval_libc_i32("PROT_WRITE");
+
+        // First, we do some basic argument validation as required by mmap
+        if (flags & (map_private | map_shared)).count_ones() != 1 {
+            this.set_last_error(Scalar::from_i32(this.eval_libc_i32("EINVAL")))?;
+            return Ok(Scalar::from_maybe_pointer(Pointer::null(), this));
+        }
+        if length == 0 {
+            this.set_last_error(Scalar::from_i32(this.eval_libc_i32("EINVAL")))?;
+            return Ok(Scalar::from_maybe_pointer(Pointer::null(), this));
+        }
+
+        // If a user tries to map a file, we want to loudly inform them that this is not going
+        // to work. It is possible that POSIX gives us enough leeway to return an error, but the
+        // outcome for the user (I need to add cfg(miri)) is the same, just more frustrating.
+        if fd != -1 {
+            throw_unsup_format!("Miri does not support file-backed memory mappings");
+        }
+
+        // POSIX says:
+        // [ENOTSUP]
+        // * MAP_FIXED or MAP_PRIVATE was specified in the flags argument and the implementation
+        // does not support this functionality.
+        // * The implementation does not support the combination of accesses requested in the
+        // prot argument.
+        //
+        // Miri doesn't support MAP_FIXED or any any protections other than PROT_READ|PROT_WRITE.
+        if flags & map_fixed != 0 || prot != prot_read | prot_write {
+            this.set_last_error(Scalar::from_i32(this.eval_libc_i32("ENOTSUP")))?;
+            return Ok(Scalar::from_maybe_pointer(Pointer::null(), this));
+        }
+
+        // Miri does not support shared mappings, or any of the other extensions that for example
+        // Linux has added to the flags arguments.
+        if flags != map_private | map_anonymous {
+            throw_unsup_format!(
+                "Miri only supports calls to mmap which set the flags argument to MAP_PRIVATE|MAP_ANONYMOUS"
+            );
+        }
+
+        // This is only used for file mappings, which we don't support anyway.
+        if offset != 0 {
+            throw_unsup_format!("Miri does not support non-zero offsets to mmap");
+        }
+
+        let align = Align::from_bytes(this.machine.page_size).unwrap();
+        let map_length = this.machine.round_up_to_multiple_of_page_size(length).unwrap_or(u64::MAX);
+
+        let ptr =
+            this.allocate_ptr(Size::from_bytes(map_length), align, MiriMemoryKind::Mmap.into())?;
+        // We just allocated this, the access is definitely in-bounds and fits into our address space.
+        // mmap guarantees new mappings are zero-init.
+        this.write_bytes_ptr(
+            ptr.into(),
+            std::iter::repeat(0u8).take(usize::try_from(map_length).unwrap()),
+        )
+        .unwrap();
+        // Memory mappings are always exposed
+        let (prov, _) = ptr.into_parts();
+        let Provenance::Concrete { alloc_id, tag } = prov else { unreachable!() };
+        intptrcast::GlobalStateInner::expose_ptr(this, alloc_id, tag)?;
+
+        Ok(Scalar::from_pointer(ptr, this))
+    }
+
+    fn mremap(
+        &mut self,
+        old_address: &OpTy<'tcx, Provenance>,
+        old_size: &OpTy<'tcx, Provenance>,
+        new_size: &OpTy<'tcx, Provenance>,
+        flags: &OpTy<'tcx, Provenance>,
+    ) -> InterpResult<'tcx, Scalar<Provenance>> {
+        let this = self.eval_context_mut();
+
+        let old_address = this.read_pointer(old_address)?;
+        let old_size = this.read_scalar(old_size)?.to_machine_usize(this)?;
+        let new_size = this.read_scalar(new_size)?.to_machine_usize(this)?;
+        let flags = this.read_scalar(flags)?.to_i32()?;
+
+        // old_address must be a multiple of the page size
+        #[allow(clippy::integer_arithmetic)] // PAGE_SIZE is nonzero
+        if old_address.addr().bytes() % this.machine.page_size != 0 || new_size == 0 {
+            this.set_last_error(Scalar::from_i32(this.eval_libc_i32("EINVAL")))?;
+            return Ok(this.eval_libc("MAP_FAILED"));
+        }
+
+        if flags & this.eval_libc_i32("MREMAP_FIXED") != 0 {
+            throw_unsup_format!("Miri does not support mremap wth MREMAP_FIXED");
+        }
+
+        if flags & this.eval_libc_i32("MREMAP_DONTUNMAP") != 0 {
+            throw_unsup_format!("Miri does not support mremap wth MREMAP_DONTUNMAP");
+        }
+
+        if flags & this.eval_libc_i32("MREMAP_MAYMOVE") == 0 {
+            // We only support MREMAP_MAYMOVE, so not passing the flag is just a failure
+            this.set_last_error(Scalar::from_i32(this.eval_libc_i32("EINVAL")))?;
+            return Ok(Scalar::from_maybe_pointer(Pointer::null(), this));
+        }
+
+        let align = this.machine.page_align();
+        let ptr = this.reallocate_ptr(
+            old_address,
+            Some((Size::from_bytes(old_size), align)),
+            Size::from_bytes(new_size),
+            align,
+            MiriMemoryKind::Mmap.into(),
+        )?;
+        if let Some(increase) = new_size.checked_sub(old_size) {
+            // We just allocated this, the access is definitely in-bounds and fits into our address space.
+            // mmap guarantees new mappings are zero-init.
+            this.write_bytes_ptr(
+                ptr.offset(Size::from_bytes(old_size), this).unwrap().into(),
+                std::iter::repeat(0u8).take(usize::try_from(increase).unwrap()),
+            )
+            .unwrap();
+        }
+        // Memory mappings are always exposed
+        let (prov, _) = ptr.into_parts();
+        let Provenance::Concrete { alloc_id, tag } = prov else { unreachable!() };
+        intptrcast::GlobalStateInner::expose_ptr(this, alloc_id, tag)?;
+
+        Ok(Scalar::from_pointer(ptr, this))
+    }
+
+    fn munmap(
+        &mut self,
+        addr: &OpTy<'tcx, Provenance>,
+        length: &OpTy<'tcx, Provenance>,
+    ) -> InterpResult<'tcx, Scalar<Provenance>> {
+        let this = self.eval_context_mut();
+
+        let addr = this.read_pointer(addr)?;
+        let length = this.read_scalar(length)?.to_machine_usize(this)?;
+
+        // addr must be a multiple of the page size
+        #[allow(clippy::integer_arithmetic)] // PAGE_SIZE is nonzero
+        if addr.addr().bytes() % this.machine.page_size != 0 {
+            this.set_last_error(Scalar::from_i32(this.eval_libc_i32("EINVAL")))?;
+            // FIXME: The man page says this returns MAP_FAILED but that is type void*, and this
+            // function returns int.
+            return Ok(Scalar::from_i32(-1));
+        }
+
+        // All pages containing a part of the indicated range are unmapped.
+        let length = this.machine.round_up_to_multiple_of_page_size(length).unwrap_or(u64::MAX);
+
+        // FIXME: POSIX says that it is unspecified whether the address range needs to be mapped,
+        // Linux is clear that it is not an error to munmap a region which is not mapped.
+        this.deallocate_ptr(
+            addr,
+            Some((Size::from_bytes(length), this.machine.page_align())),
+            MiriMemoryKind::Mmap.into(),
+        )?;
+        Ok(Scalar::from_i32(0))
+    }
+}

src/shims/unix/mod.rs

@@ -2,6 +2,7 @@ pub mod dlsym;
 pub mod foreign_items;
 
 mod fs;
+mod mem;
 mod sync;
 mod thread;
 

tests/fail/mmap_invalid_dealloc.rs

@@ -0,0 +1,18 @@
+//@compile-flags: -Zmiri-disable-isolation
+//@ignore-target-windows: No libc on Windows
+
+#![feature(rustc_private)]
+
+fn main() {
+    unsafe {
+        let ptr = libc::mmap(
+            std::ptr::null_mut(),
+            4096,
+            libc::PROT_READ | libc::PROT_WRITE,
+            libc::MAP_PRIVATE | libc::MAP_ANONYMOUS,
+            -1,
+            0,
+        );
+        libc::free(ptr); //~ ERROR: which is mmap memory, using C heap deallocation operation
+    }
+}

tests/fail/mmap_invalid_dealloc.stderr

@@ -0,0 +1,15 @@
+error: Undefined Behavior: deallocating ALLOC, which is mmap memory, using C heap deallocation operation
+  --> $DIR/mmap_invalid_dealloc.rs:LL:CC
+   |
+LL |         libc::free(ptr);
+   |         ^^^^^^^^^^^^^^^ deallocating ALLOC, which is mmap memory, using C heap deallocation operation
+   |
+   = help: this indicates a bug in the program: it performed an invalid operation, and caused Undefined Behavior
+   = help: see https://doc.rust-lang.org/nightly/reference/behavior-considered-undefined.html for further information
+   = note: BACKTRACE:
+   = note: inside `main` at $DIR/mmap_invalid_dealloc.rs:LL:CC
+
+note: some details are omitted, run with `MIRIFLAGS=-Zmiri-backtrace=full` for a verbose backtrace
+
+error: aborting due to previous error
+