Introduce umode binary and map it in salus user space address. #178

glg-rv · 2022-12-09T18:24:36Z

This PR includes a umode and libuser library (taken from Dylan's branch). These are just stubs at the moment, but they do create a risc-v elf binary that can be used as a basis for future userspace work.

It also introduces riscv-elf. A super simple ELF library tailored to our needs, with no memory allocation and focused on loading elf. Care has been taken in checking the validity of file offset before accessing them.

It then proceed to extend HypMap to allow a new type of region to be loaded. Specifically, it's a region that needs to be allocated and populated with existing data.

With this patch, the ELF is loaded in userspace, and there's a copy of the whole elf for each CPU. Current abstraction can be changed though to share .text and .rodata across CPUs. Although the big batch of memory (.data and .stack) will always be per-cpu.

lds/umode.lds

abrestic-rivos · 2022-12-09T18:53:36Z

lds/umode.lds

+
+    .stack : ALIGN(4096) {
+        PROVIDE(_stack_start = .);
+        . += 4096;


Is 4kB going to be enough?

No but can be changed quite easily. This is just for the stub.

Ok, can we put some space between the bss and the stack so that we get a page fault when we inevitably hit that case?

As per inevitably, once we get an actual binary doing something the linking would've been changed.

Updated. Got rid of MEMORY command as it influences the way ld finds the next available address when assigning a section to a memory region.

Now there's an empty 4k section between the end of BSS and stack.

riscv-elf/src/lib.rs

abrestic-rivos · 2022-12-09T18:58:52Z

riscv-elf/src/lib.rs

+    fn as_usize(&self) -> Option<usize> {
+        self.inner.try_into().ok()
+    }


We're assuming 64-bit everywhere else in the module, so I don't really see a problem assuming usize == u64 here too :)

Sure. I went for paranoia in this code.

Changed. as_usize() returns usize. (with a comment).

abrestic-rivos · 2022-12-09T20:06:24Z

src/hyp_map.rs

 }

 impl HypMap {
    /// Create a new hypervisor map from a hardware memory mem map.
-    pub fn new(mem_map: HwMemMap) -> HypMap {
-        let regions = mem_map
+    pub fn new(mem_map: HwMemMap, elf_map: ElfMap) -> HypMap {


s/elf_map/user_map (or umode_map)?

if I have to chose (and not chose elf_map, i'll go for user_map. :-)

Changed to user_map.

abrestic-rivos · 2022-12-09T20:08:11Z

src/hyp_map.rs

+    // Data to be populated in the VA area
+    data: Vec<u8>,


Can we avoid this extra memcpy() from the ELF to this temporary buffer?

You're describing my Thursday night. Originally I had kept the reference from 'elf to here. It is sane because afterall the elf is 'static. But turns out that at least I couldn't understand how to let Rust understand in a non convoluted way that there were to lifetimes here, one of the underlying data structure and the other of the user_map.

In general the structure needs to have a life time, the code becomes much much harder to follow and should essentially hold the ElfMap in it to keep the reference lifetime valid. Just over complication for a language that clearly doesn't like these sort of things.

This would also remove generality to the whole concept of a populated region.

In general, much more complicated code, to save a few kbs of RAM.

I think you had your lifetimes backwards in ElfMap::segments(). With that fixed, this becomes pretty straightforward, see https://github.com/abrestic-rivos/salus/tree/for-glg/user_mode

Whops. That's a few hours of my life I'll never get back. Thank you!

Changed to your code. Thanks again.

abrestic-rivos · 2022-12-09T20:08:50Z

src/main.rs

@@ -459,8 +449,34 @@ extern "C" fn kernel_init(hart_id: u64, fdt_addr: u64) {
    let guest_phys_size = mem_map.regions().last().unwrap().end().bits()
        - mem_map.regions().next().unwrap().base().bits();

+    // Parse the user-mode ELF containing the user-mode task.
+    let user_elf = include_bytes!("../target/riscv64gc-unknown-none-elf/release/umode");


Ugh, this is gross but I don't immediately have a better suggestion.

Yes, it is indefensible but also the best thing we can do now. Double-checked with @dgreid about this as well.

yes, it's just a hack until we figure out a better build system. I'm hoping to let zach and tom figure out blaze for hubris tasks then copy that.

glg-rv · 2022-12-10T06:41:12Z

Simplified HypMapPopulatedRegion. As segments are aligned to 4k we can eliminate the offset. This in turns makes everything simpler.

abrestic-rivos

LGTM, thanks!

abrestic-rivos · 2022-12-12T14:56:49Z

libuser/src/task_start.S

+    la t1, task_main
+    la ra, 1f
+    jr t1
+
+    j 1f
+1:


Just call task_main is sufficient.

Ah good catch. Had a note somewhere when I saw your patches to change this too. Thanks!

Fixed.

abrestic-rivos · 2022-12-12T14:57:57Z

lds/umode.lds

+
+    .stack : ALIGN(4096) {
+        PROVIDE(_stack_start = .);
+        . += 4096;


Ok, can we put some space between the bss and the stack so that we get a page fault when we inevitably hit that case?

This patch introduces stub userspace binary and library for salus. Currently the code is compiled but unused. Original code by Dylan, with minor changes from me. Signed-off-by: Dylan Reid <[email protected]> Signed-off-by: Gianluca Guida <[email protected]>

glg-rv · 2022-12-12T21:00:03Z

Added a fix to load Program Headers that have no data in file.

riscv-elf is a library to parse an elf file in memory in Rust. It is esplicitly tailored to salus and riscv. Work has been done (mainly through fuzzing) to check that the library can handle malformed ELF functions. It is a simple library focused on loading an elf. Its main use is to return an `ElfSegment` iterator that mirrors the Program Header section and its data content. Signed-off-by: Gianluca Guida <[email protected]>

Signed-off-by: Gianluca Guida <[email protected]>

This patch allows to map the `umode` binary into salus address space. More work might be needed for a better build system and integration of the umode binary into salus. Signed-off-by: Gianluca Guida <[email protected]>

glg-rv force-pushed the topic/user_mode branch from 24bc469 to ac2859a Compare December 9, 2022 18:32

abrestic-rivos reviewed Dec 9, 2022

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glg-rv force-pushed the topic/user_mode branch from ac2859a to bb182f4 Compare December 10, 2022 03:46

glg-rv mentioned this pull request Dec 10, 2022

Map salus in the top half of the VA space. #180

Open

glg-rv force-pushed the topic/user_mode branch from bb182f4 to 7bef103 Compare December 10, 2022 06:38

abrestic-rivos approved these changes Dec 12, 2022

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glg-rv force-pushed the topic/user_mode branch 2 times, most recently from ca212f7 to e8a264c Compare December 12, 2022 20:58

glg-rv added 3 commits December 12, 2022 22:28

riscv-page-tables: Define user mode PTEs flags

595bfaa

Signed-off-by: Gianluca Guida <[email protected]>

Map user-mode ELF in Salus address space.

2be9b68

This patch allows to map the `umode` binary into salus address space. More work might be needed for a better build system and integration of the umode binary into salus. Signed-off-by: Gianluca Guida <[email protected]>

glg-rv force-pushed the topic/user_mode branch from e8a264c to 2be9b68 Compare December 12, 2022 22:30

abrestic-rivos merged commit 2eef428 into rivosinc:main Dec 13, 2022

abrestic-rivos had a problem deploying to github-pages December 13, 2022 03:20 — with GitHub Actions Failure

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Introduce umode binary and map it in salus user space address. #178

Introduce umode binary and map it in salus user space address. #178

glg-rv commented Dec 9, 2022

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Introduce umode binary and map it in salus user space address. #178

Introduce umode binary and map it in salus user space address. #178

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glg-rv commented Dec 9, 2022

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glg-rv commented Dec 10, 2022

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glg-rv commented Dec 12, 2022