diff options
Diffstat (limited to 'tools/testing/selftests/powerpc/mm/large_vm_gpr_corruption.c')
| -rw-r--r-- | tools/testing/selftests/powerpc/mm/large_vm_gpr_corruption.c | 158 |
1 files changed, 158 insertions, 0 deletions
diff --git a/tools/testing/selftests/powerpc/mm/large_vm_gpr_corruption.c b/tools/testing/selftests/powerpc/mm/large_vm_gpr_corruption.c new file mode 100644 index 000000000000..7da515f1da72 --- /dev/null +++ b/tools/testing/selftests/powerpc/mm/large_vm_gpr_corruption.c @@ -0,0 +1,158 @@ +// SPDX-License-Identifier: GPL-2.0+ +// +// Copyright 2022, Michael Ellerman, IBM Corp. +// +// Test that the 4PB address space SLB handling doesn't corrupt userspace registers +// (r9-r13) due to a SLB fault while saving the PPR. +// +// The bug was introduced in f384796c4 ("powerpc/mm: Add support for handling > 512TB +// address in SLB miss") and fixed in 4c2de74cc869 ("powerpc/64: Interrupts save PPR on +// stack rather than thread_struct"). +// +// To hit the bug requires the task struct and kernel stack to be in different segments. +// Usually that requires more than 1TB of RAM, or if that's not practical, boot the kernel +// with "disable_1tb_segments". +// +// The test works by creating mappings above 512TB, to trigger the large address space +// support. It creates 64 mappings, double the size of the SLB, to cause SLB faults on +// each access (assuming naive replacement). It then loops over those mappings touching +// each, and checks that r9-r13 aren't corrupted. +// +// It then forks another child and tries again, because a new child process will get a new +// kernel stack and thread struct allocated, which may be more optimally placed to trigger +// the bug. It would probably be better to leave the previous child processes hanging +// around, so that kernel stack & thread struct allocations are not reused, but that would +// amount to a 30 second fork bomb. The current design reliably triggers the bug on +// unpatched kernels. + +#include <signal.h> +#include <stdio.h> +#include <stdlib.h> +#include <sys/mman.h> +#include <sys/types.h> +#include <sys/wait.h> +#include <unistd.h> + +#include "utils.h" + +#ifndef MAP_FIXED_NOREPLACE +#define MAP_FIXED_NOREPLACE MAP_FIXED // "Should be safe" above 512TB +#endif + +#define BASE_ADDRESS (1ul << 50) // 1PB +#define STRIDE (2ul << 40) // 2TB +#define SLB_SIZE 32 +#define NR_MAPPINGS (SLB_SIZE * 2) + +static volatile sig_atomic_t signaled; + +static void signal_handler(int sig) +{ + signaled = 1; +} + +#define CHECK_REG(_reg) \ + if (_reg != _reg##_orig) { \ + printf(str(_reg) " corrupted! Expected 0x%lx != 0x%lx\n", _reg##_orig, \ + _reg); \ + _exit(1); \ + } + +static int touch_mappings(void) +{ + unsigned long r9_orig, r10_orig, r11_orig, r12_orig, r13_orig; + unsigned long r9, r10, r11, r12, r13; + unsigned long addr, *p; + int i; + + for (i = 0; i < NR_MAPPINGS; i++) { + addr = BASE_ADDRESS + (i * STRIDE); + p = (unsigned long *)addr; + + asm volatile("mr %0, %%r9 ;" // Read original GPR values + "mr %1, %%r10 ;" + "mr %2, %%r11 ;" + "mr %3, %%r12 ;" + "mr %4, %%r13 ;" + "std %10, 0(%11) ;" // Trigger SLB fault + "mr %5, %%r9 ;" // Save possibly corrupted values + "mr %6, %%r10 ;" + "mr %7, %%r11 ;" + "mr %8, %%r12 ;" + "mr %9, %%r13 ;" + "mr %%r9, %0 ;" // Restore original values + "mr %%r10, %1 ;" + "mr %%r11, %2 ;" + "mr %%r12, %3 ;" + "mr %%r13, %4 ;" + : "=&b"(r9_orig), "=&b"(r10_orig), "=&b"(r11_orig), + "=&b"(r12_orig), "=&b"(r13_orig), "=&b"(r9), "=&b"(r10), + "=&b"(r11), "=&b"(r12), "=&b"(r13) + : "b"(i), "b"(p) + : "r9", "r10", "r11", "r12", "r13"); + + CHECK_REG(r9); + CHECK_REG(r10); + CHECK_REG(r11); + CHECK_REG(r12); + CHECK_REG(r13); + } + + return 0; +} + +static int test(void) +{ + unsigned long page_size, addr, *p; + struct sigaction action; + bool hash_mmu; + int i, status; + pid_t pid; + + // This tests a hash MMU specific bug. + FAIL_IF(using_hash_mmu(&hash_mmu)); + SKIP_IF(!hash_mmu); + // 4K kernels don't support 4PB address space + SKIP_IF(sysconf(_SC_PAGESIZE) < 65536); + + page_size = sysconf(_SC_PAGESIZE); + + for (i = 0; i < NR_MAPPINGS; i++) { + addr = BASE_ADDRESS + (i * STRIDE); + + p = mmap((void *)addr, page_size, PROT_READ | PROT_WRITE, + MAP_PRIVATE | MAP_ANONYMOUS | MAP_FIXED_NOREPLACE, -1, 0); + if (p == MAP_FAILED) { + perror("mmap"); + printf("Error: couldn't mmap(), confirm kernel has 4PB support?\n"); + return 1; + } + } + + action.sa_handler = signal_handler; + action.sa_flags = SA_RESTART; + FAIL_IF(sigaction(SIGALRM, &action, NULL) < 0); + + // Seen to always crash in under ~10s on affected kernels. + alarm(30); + + while (!signaled) { + // Fork new processes, to increase the chance that we hit the case where + // the kernel stack and task struct are in different segments. + pid = fork(); + if (pid == 0) + exit(touch_mappings()); + + FAIL_IF(waitpid(-1, &status, 0) == -1); + FAIL_IF(WIFSIGNALED(status)); + FAIL_IF(!WIFEXITED(status)); + FAIL_IF(WEXITSTATUS(status)); + } + + return 0; +} + +int main(void) +{ + return test_harness(test, "large_vm_gpr_corruption"); +} |