Fix bpf2bpf local function calls with stack usage

[dthaler]

Turns out clang/gcc generate code that depends on r10 being updated by the platform across function calls. This PR corrects the verifier to have the expected behavior and tests it with an actual sample ELF generated by clang.

Summary by CodeRabbit

• New Features

  • Updated test cases for local function calls, recursion, and stack manipulation, enhancing error handling and state preservation.
  • Added new test cases for subtraction operations involving various types of registers and pointers, improving error messaging and validation.

• Bug Fixes

  • Improved handling of stack and memory operations in the ebpf_domain_t class, simplifying access checks and ensuring correct memory management.

• Refactor

  • Simplified method signatures by removing unnecessary parameters, enhancing clarity and usability.

• Documentation

  • Updated error messages in test cases for clarity, particularly regarding stack access and subtraction operations.

[coderabbitai]

Walkthrough

The changes in this pull request involve updates to the ebpf-samples subproject commit reference, modifications to the return logic of functions in src/asm_ostream.hpp, changes to the return type in src/asm_syntax.hpp, and refinements in the ebpf_domain_t class methods in src/crab/ebpf_domain.cpp and src/crab/ebpf_domain.hpp. Additionally, new test cases related to local function calls and stack manipulation have been added in test-data/calllocal.yaml.

Changes

File	Change Summary
ebpf-samples	Subproject commit updated: 325cce1bc528a8b70e02ea914d407b4e4f89731d → 33f01fafa414520ad56ab219db343422bb655b32
src/asm_ostream.hpp	Modified label_to_offset16 and label_to_offset32 functions to use conditional expressions for return values.
src/asm_syntax.hpp	Updated call_stack_depth method to explicitly use gsl::narrow<int> for return type instead of implicit conversion.
src/crab/ebpf_domain.cpp	Simplified check_access_stack method by removing call_stack_depth parameter; adjusted stack access logic and updated do_load_stack and do_store_stack methods.
src/crab/ebpf_domain.hpp	Updated check_access_stack method signature to remove call_stack_depth parameter.
test-data/calllocal.yaml	Added multiple test cases for local function calls, recursion, and stack manipulation, including handling of nested calls and error scenarios for excessive recursion.
test-data/stack.yaml	Updated error message for invalid stack access to clarify conditions for valid access.
test-data/subtract.yaml	Added and modified test cases related to subtraction operations, including new conditions and error messages for pointer types and bounds.

Possibly related PRs

• Put bpf2bpf caller in a named section #714: Updates the subproject commit reference for ebpf-samples, directly related to this PR.
• Update test that used to fail to pass #735: Similar to PR Put bpf2bpf caller in a named section #714, also updates the subproject commit reference for ebpf-samples.
• Fix ebpf_base.h usability in C #777: Modifies constants in ebpf_base.h, which may indirectly relate to the overall structure and usability of the eBPF framework, including how subprojects like ebpf-samples are utilized.
• Fix overflow in conversion from uvalue to svalue #769: Changes in arithmetic operations and overflow handling in ebpf_domain_t could be relevant to the overall functionality of the eBPF verifier, which may interact with the ebpf-samples subproject.
• Don't permit truncating non-numbers #772: Focus on preventing truncation of non-numeric values may relate to the robustness of the eBPF verifier, impacting how the ebpf-samples are processed.
• Make the assertions part of a generalized instruction #779: Integration of assertions into instructions enhances the functionality of the eBPF verifier, relevant to the overall framework that includes ebpf-samples.

🐇 In the land of code, where rabbits hop,
Changes abound, and we never stop.
From stacks to calls, we refine with care,
Each test a tale, in the code we share.
With every update, our project grows bright,
Hopping along, in the soft moonlight! 🌙✨

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📜 Recent review details

Configuration used: CodeRabbit UI
Review profile: ASSERTIVE

📥 Commits

Reviewing files that changed from the base of the PR and between 3f58c29 and ed32a06.

📒 Files selected for processing (3)

• ebpf-samples (1 hunks)
• test-data/stack.yaml (1 hunks)
• test-data/subtract.yaml (1 hunks)

🔇 Additional comments (3)

ebpf-samples (1)

1-1: Verify dependency and commit existence.

The subproject commit update aligns with the PR objectives to include test cases for bpf2bpf local function calls.

Let's verify the dependency and commit:

test-data/subtract.yaml (1)

162-162: LGTM! The new error message enhances stack bounds validation.

The added error message properly complements the existing upper bound check by ensuring the lower bound of stack access stays within the subprogram's stack frame. This aligns well with the PR's objective of fixing stack usage in bpf2bpf local function calls.

Let's verify the consistency of stack size constants across the codebase:

✅ Verification successful

Stack size constants and bound checks are consistently defined and used across the codebase

The verification shows that:

• EBPF_SUBPROGRAM_STACK_SIZE is defined as 512 bytes in src/ebpf_base.h
• The error message in test-data/subtract.yaml matches the implementation in src/crab/ebpf_domain.cpp
• Stack bound checks are consistently enforced:
  • Lower bound: r10.stack_offset - EBPF_SUBPROGRAM_STACK_SIZE
  • Upper bound: EBPF_TOTAL_STACK_SIZE

🏁 Scripts executed

The following scripts were executed for the analysis:

Script:

#!/bin/bash
# Description: Verify stack size constants are consistently defined and used
# Expected: Find definitions of EBPF_TOTAL_STACK_SIZE and EBPF_SUBPROGRAM_STACK_SIZE
# and their usage in stack bound checks

# Search for stack size constant definitions
echo "=== Stack size constant definitions ==="
rg "EBPF_(TOTAL|SUBPROGRAM)_STACK_SIZE"

# Search for stack bound checking patterns
echo "=== Stack bound checking patterns ==="
rg "r10\.stack_offset.*EBPF.*STACK_SIZE"

Length of output: 5237

test-data/stack.yaml (1)

597-597: LGTM! Error message simplified to better reflect platform behavior.

The updated error message now directly references EBPF_SUBPROGRAM_STACK_SIZE instead of including call stack depth in the calculation. This change aligns well with the PR's objective of modifying the verifier to match platform behavior regarding r10 register updates during function calls.

---

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[coveralls]

coverage: 90.532% (+0.002%) from 90.53%
when pulling ed32a06 on dthaler:bpf2bpf-stack
into 71a34c7 on vbpf:main.