openrisc: fix arbitrary kernel memory access via or1k_atomic syscallgrafted

sys_or1k_atomic() (syscall 244 in the "or1k" ABI) takes two user
pointers, v1 and v2, and swaps the words they point to in hand-written
assembly.

    l.lwz   r29,0(r4)
    l.lwz   r27,0(r5)
    l.sw    0(r4),r27
    l.sw    0(r5),r29

The pointers are not checked with access_ok(). The four memory
accesses also have no exception table entries.

A caller passes a kernel address as either pointer, and the syscall
reads from and writes to it directly.

This gives an unprivileged process a kernel read/write primitive. It
overwrites kernel data such as the sys_call_table, gaining code
execution in kernel context.

Check both pointers before entering the critical section. Add fixups
for the four memory accesses so faults on valid but unmapped user
addresses return -EFAULT.

[shorne@gmail.com: fix comment style]
Fixes: 9d02a4283e9c ("OpenRISC: Boot code")
Cc: stable@vger.kernel.org
Signed-off-by: Ali Ahmet Memis <ali@iusegentoo.com>
Signed-off-by: Stafford Horne <shorne@gmail.com>

1 files changed, 115 insertions, 0 deletions

diff --git a/tools/testing/memblock/README b/tools/testing/memblock/README
new file mode 100644
index 000000000..b435f48d8
--- /dev/null
+++ b/tools/testing/memblock/README
@@ -0,0 +1,115 @@
+==================
+Memblock simulator
+==================
+
+Introduction
+============
+
+Memblock is a boot time memory allocator[1] that manages memory regions before
+the actual memory management is initialized. Its APIs allow to register physical
+memory regions, mark them as available or reserved, allocate a block of memory
+within the requested range and/or in specific NUMA node, and many more.
+
+Because it is used so early in the booting process, testing and debugging it is
+difficult. This test suite, usually referred as memblock simulator, is
+an attempt at testing the memblock mechanism. It runs one monolithic test that
+consist of a series of checks that exercise both the basic operations and
+allocation functionalities of memblock. The main data structure of the boot time
+memory allocator is initialized at the build time, so the checks here reuse its
+instance throughout the duration of the test. To ensure that tests don't affect
+each other, region arrays are reset in between.
+
+As this project uses the actual memblock code and has to run in user space,
+some of the kernel definitions were stubbed by the initial commit that
+introduced memblock simulator (commit 16802e55dea9 ("memblock tests: Add
+skeleton of the memblock simulator")) and a few preparation commits just
+before it. Most of them don't match the kernel implementation, so one should
+consult them first before making any significant changes to the project.
+
+Usage
+=====
+
+To run the tests, build the main target and run it:
+
+$ make && ./main
+
+A successful run produces no output. It is possible to control the behavior
+by passing options from command line. For example, to include verbose output,
+append the `-v` options when you run the tests:
+
+$ ./main -v
+
+This will print information about which functions are being tested and the
+number of test cases that passed.
+
+For the full list of options from command line, see `./main --help`.
+
+It is also possible to override different configuration parameters to change
+the test functions. For example, to simulate enabled NUMA, use:
+
+$ make NUMA=1
+
+For the full list of build options, see `make help`.
+
+Project structure
+=================
+
+The project has one target, main, which calls a group of checks for basic and
+allocation functions. Tests for each group are defined in dedicated files, as it
+can be seen here:
+
+memblock
+|-- asm       ------------------,
+|-- lib                         |-- implement function and struct stubs
+|-- linux     ------------------'
+|-- scripts
+|    |-- Makefile.include        -- handles `make` parameters
+|-- tests
+|    |-- alloc_api.(c|h)         -- memblock_alloc tests
+|    |-- alloc_helpers_api.(c|h) -- memblock_alloc_from tests
+|    |-- alloc_nid_api.(c|h)     -- memblock_alloc_try_nid tests
+|    |-- basic_api.(c|h)         -- memblock_add/memblock_reserve/... tests
+|    |-- common.(c|h)            -- helper functions for resetting memblock;
+|-- main.c        --------------.   dummy physical memory definition
+|-- Makefile                     `- test runner
+|-- README
+|-- TODO
+|-- .gitignore
+
+Simulating physical memory
+==========================
+
+Some allocation functions clear the memory in the process, so it is required for
+memblock to track valid memory ranges. To achieve this, the test suite registers
+with memblock memory stored by test_memory struct. It is a small wrapper that
+points to a block of memory allocated via malloc. For each group of allocation
+tests, dummy physical memory is allocated, added to memblock, and then released
+at the end of the test run. The structure of a test runner checking allocation
+functions is as follows:
+
+int memblock_alloc_foo_checks(void)
+{
+	reset_memblock_attributes();     /* data structure reset */
+	dummy_physical_memory_init();    /* allocate and register memory */
+
+	(...allocation checks...)
+
+	dummy_physical_memory_cleanup(); /* free the memory */
+}
+
+There's no need to explicitly free the dummy memory from memblock via
+memblock_free() call. The entry will be erased by reset_memblock_regions(),
+called at the beginning of each test.
+
+Known issues
+============
+
+1. Tests for memblock_alloc_low() can't be easily implemented. The function uses
+   ARCH_LOW_ADDRESS_LIMIT marco, which can't be changed to point at the low
+   memory of the memory_block.
+
+References
+==========
+
+1. Boot time memory management documentation page:
+   https://www.kernel.org/doc/html/latest/core-api/boot-time-mm.html