Manually flush stack pages after populating them

We'd prefer to unmap the pages, but we can't (See #53). Instead directly flush
them, to be sure the stack is visible in the target process.

src/arch/aarch64/mod.rs

@@ -3,6 +3,7 @@ use core::marker::PhantomData;
 use typenum::*;
 
 use crate::cap::{page_state, Page, PageTable, PhantomCap};
+use crate::error::{ErrorExt, SeL4Error};
 use crate::vspace::{PagingRec, PagingTop};
 
 pub mod cap;
@@ -145,3 +146,11 @@ pub mod vm_attributes {
 
     pub const PROGRAM_DATA: VMAttributes = PAGE_CACHEABLE | PARITY_ENABLED | EXECUTE_NEVER;
 }
+
+pub(crate) unsafe fn flush_page(cptr: usize) -> Result<(), SeL4Error> {
+    selfe_sys::seL4_ARM_Page_CleanInvalidate_Data(cptr, 0x0000, PageBytes::USIZE)
+        .as_result()
+        .map_err(|e| SeL4Error::PageCleanInvalidateData(e))?;
+
+    Ok(())
+}

src/arch/arm/mod.rs

@@ -1,3 +1,4 @@
+use crate::error::{ErrorExt, SeL4Error};
 use typenum::*;
 
 pub mod cap;
@@ -135,3 +136,11 @@ pub mod vm_attributes {
 
     pub const PROGRAM_DATA: VMAttributes = PAGE_CACHEABLE | PARITY_ENABLED | EXECUTE_NEVER;
 }
+
+pub(crate) unsafe fn flush_page(cptr: usize) -> Result<(), SeL4Error> {
+    selfe_sys::seL4_ARM_Page_CleanInvalidate_Data(cptr, 0x0000, PageBytes::USIZE)
+        .as_result()
+        .map_err(|e| SeL4Error::PageCleanInvalidateData(e))?;
+
+    Ok(())
+}

src/cap/mod.rs

@@ -148,6 +148,19 @@ impl<CT: CapType, Role: CNodeRole, Slots: Unsigned> CapRange<CT, Role, Slots> {
         }
     }
 
+    pub(crate) fn for_each<F: Fn(&Cap<CT, Role>) -> ()>(&self, f: F)
+    where
+        CT: CapRangeDataReconstruction,
+    {
+        for index in (0..self.len()) {
+            f(&Cap {
+                cptr: self.start_cptr + index,
+                _role: PhantomData,
+                cap_data: CT::reconstruct(index, &self.start_cap_data),
+            })
+        }
+    }
+
     pub(crate) fn into_iter(self) -> impl Iterator<Item = Cap<CT, Role>>
     where
         CT: CapRangeDataReconstruction,

src/userland/process/self_hosted.rs

@@ -109,7 +109,7 @@ impl<StackBitSize: Unsigned> SelfHostedProcess<StackBitSize> {
 
         // Map the stack to the target address space
         let stack_top = parent_mapped_region.vaddr() + parent_mapped_region.size_bytes();
-        let (unmapped_stack_pages, _) =
+        let (unmapped_stack_pages, local_stack_pages) =
             parent_mapped_region.share(stack_slots, parent_cnode, CapRights::RW)?;
         let mapped_stack_pages = vspace.map_shared_region_and_consume(
             unmapped_stack_pages,
@@ -150,6 +150,8 @@ impl<StackBitSize: Unsigned> SelfHostedProcess<StackBitSize> {
         let stack_pointer =
             mapped_stack_pages.vaddr() + mapped_stack_pages.size_bytes() - param_size_on_stack;
 
+        local_stack_pages.flush()?;
+
         registers.sp = stack_pointer;
         registers.pc = self_hosted_run::<T> as usize;
 

src/userland/process/standard.rs

@@ -100,7 +100,7 @@ impl<StackBitSize: Unsigned> StandardProcess<StackBitSize> {
 
         // Map the stack to the target address space
         let stack_top = parent_mapped_region.vaddr() + parent_mapped_region.size_bytes();
-        let (unmapped_stack_pages, _): (UnmappedMemoryRegion<StackBitSize, _>, _) =
+        let (unmapped_stack_pages, local_stack_pages): (UnmappedMemoryRegion<StackBitSize, _>, _) =
             parent_mapped_region.share(stack_slots, parent_cnode, CapRights::RW)?;
         let mapped_stack_pages = vspace.map_shared_region_and_consume(
             unmapped_stack_pages,
@@ -119,6 +119,8 @@ impl<StackBitSize: Unsigned> StandardProcess<StackBitSize> {
             )
         };
 
+        local_stack_pages.flush()?;
+
         let stack_pointer =
             mapped_stack_pages.vaddr() + mapped_stack_pages.size_bytes() - param_size_on_stack;
 

src/vspace/region.rs

@@ -4,7 +4,7 @@ use core::ops::Sub;
 use typenum::*;
 
 use super::{KernelRetypeFanOutLimit, NumPages, VSpaceError};
-use crate::arch::PageBits;
+use crate::arch::{self, PageBits};
 use crate::cap::{
     memory_kind, page_state, role, CNode, CNodeRole, CNodeSlots, Cap, CapRange, InternalASID,
     LocalCNodeSlots, LocalCap, MemoryKind, Page, PageState, RetypeError, Untyped, WCNodeSlots,
@@ -270,6 +270,14 @@ where
         unsafe { core::slice::from_raw_parts_mut(self.vaddr() as *mut u8, self.size_bytes()) }
     }
 
+    pub fn flush(&self) -> Result<(), SeL4Error> {
+        self.caps.for_each(|cap| {
+            unsafe { arch::flush_page(cap.cptr) }.unwrap();
+        });
+
+        Ok(())
+    }
+
     #[cfg(feature = "test_support")]
     /// Super dangerous copy-aliasing
     pub(crate) unsafe fn dangerous_internal_alias(&mut self) -> Self {