From: Michael Ellerman mpe@ellerman.id.au

[ Upstream commit a8968521cfdc3e339fe69473d6632e0aa8d7202a ]

We have a general signal fuzzer, sigfuz, which can modify the MSR & NIP before sigreturn. But the chance of it hitting a kernel address and also clearing MSR_PR is fairly slim.

So add a specific test of sigreturn to a kernel address, both with and without attempting to clear MSR_PR (which the kernel must block).

Signed-off-by: Michael Ellerman mpe@ellerman.id.au Link: https://lore.kernel.org/r/20211209115944.4062384-1-mpe@ellerman.id.au Signed-off-by: Sasha Levin sashal@kernel.org --- .../selftests/powerpc/signal/.gitignore | 1 + .../testing/selftests/powerpc/signal/Makefile | 1 + .../powerpc/signal/sigreturn_kernel.c | 132 ++++++++++++++++++ 3 files changed, 134 insertions(+) create mode 100644 tools/testing/selftests/powerpc/signal/sigreturn_kernel.c

diff --git a/tools/testing/selftests/powerpc/signal/.gitignore b/tools/testing/selftests/powerpc/signal/.gitignore index ce3375cd8e73e..8f6c816099a48 100644 --- a/tools/testing/selftests/powerpc/signal/.gitignore +++ b/tools/testing/selftests/powerpc/signal/.gitignore @@ -4,3 +4,4 @@ signal_tm sigfuz sigreturn_vdso sig_sc_double_restart +sigreturn_kernel diff --git a/tools/testing/selftests/powerpc/signal/Makefile b/tools/testing/selftests/powerpc/signal/Makefile index d6ae54663aed7..84e201572466d 100644 --- a/tools/testing/selftests/powerpc/signal/Makefile +++ b/tools/testing/selftests/powerpc/signal/Makefile @@ -1,5 +1,6 @@ # SPDX-License-Identifier: GPL-2.0 TEST_GEN_PROGS := signal signal_tm sigfuz sigreturn_vdso sig_sc_double_restart +TEST_GEN_PROGS += sigreturn_kernel

CFLAGS += -maltivec $(OUTPUT)/signal_tm: CFLAGS += -mhtm diff --git a/tools/testing/selftests/powerpc/signal/sigreturn_kernel.c b/tools/testing/selftests/powerpc/signal/sigreturn_kernel.c new file mode 100644 index 0000000000000..0a1b6e591eeed --- /dev/null +++ b/tools/testing/selftests/powerpc/signal/sigreturn_kernel.c @@ -0,0 +1,132 @@ +// SPDX-License-Identifier: GPL-2.0 +/* + * Test that we can't sigreturn to kernel addresses, or to kernel mode. + */ + +#define _GNU_SOURCE + +#include <stdio.h> +#include <signal.h> +#include <stdlib.h> +#include <sys/types.h> +#include <sys/wait.h> +#include <unistd.h> + +#include "utils.h" + +#define MSR_PR (1ul << 14) + +static volatile unsigned long long sigreturn_addr; +static volatile unsigned long long sigreturn_msr_mask; + +static void sigusr1_handler(int signo, siginfo_t *si, void *uc_ptr) +{ + ucontext_t *uc = (ucontext_t *)uc_ptr; + + if (sigreturn_addr) + UCONTEXT_NIA(uc) = sigreturn_addr; + + if (sigreturn_msr_mask) + UCONTEXT_MSR(uc) &= sigreturn_msr_mask; +} + +static pid_t fork_child(void) +{ + pid_t pid; + + pid = fork(); + if (pid == 0) { + raise(SIGUSR1); + exit(0); + } + + return pid; +} + +static int expect_segv(pid_t pid) +{ + int child_ret; + + waitpid(pid, &child_ret, 0); + FAIL_IF(WIFEXITED(child_ret)); + FAIL_IF(!WIFSIGNALED(child_ret)); + FAIL_IF(WTERMSIG(child_ret) != 11); + + return 0; +} + +int test_sigreturn_kernel(void) +{ + struct sigaction act; + int child_ret, i; + pid_t pid; + + act.sa_sigaction = sigusr1_handler; + act.sa_flags = SA_SIGINFO; + sigemptyset(&act.sa_mask); + + FAIL_IF(sigaction(SIGUSR1, &act, NULL)); + + for (i = 0; i < 2; i++) { + // Return to kernel + sigreturn_addr = 0xcull << 60; + pid = fork_child(); + expect_segv(pid); + + // Return to kernel virtual + sigreturn_addr = 0xc008ull << 48; + pid = fork_child(); + expect_segv(pid); + + // Return out of range + sigreturn_addr = 0xc010ull << 48; + pid = fork_child(); + expect_segv(pid); + + // Return to no-man's land, just below PAGE_OFFSET + sigreturn_addr = (0xcull << 60) - (64 * 1024); + pid = fork_child(); + expect_segv(pid); + + // Return to no-man's land, above TASK_SIZE_4PB + sigreturn_addr = 0x1ull << 52; + pid = fork_child(); + expect_segv(pid); + + // Return to 0xd space + sigreturn_addr = 0xdull << 60; + pid = fork_child(); + expect_segv(pid); + + // Return to 0xe space + sigreturn_addr = 0xeull << 60; + pid = fork_child(); + expect_segv(pid); + + // Return to 0xf space + sigreturn_addr = 0xfull << 60; + pid = fork_child(); + expect_segv(pid); + + // Attempt to set PR=0 for 2nd loop (should be blocked by kernel) + sigreturn_msr_mask = ~MSR_PR; + } + + printf("All children killed as expected\n"); + + // Don't change address, just MSR, should return to user as normal + sigreturn_addr = 0; + sigreturn_msr_mask = ~MSR_PR; + pid = fork_child(); + waitpid(pid, &child_ret, 0); + FAIL_IF(!WIFEXITED(child_ret)); + FAIL_IF(WIFSIGNALED(child_ret)); + FAIL_IF(WEXITSTATUS(child_ret) != 0); + + return 0; +} + +int main(void) +{ + return test_harness(test_sigreturn_kernel, "sigreturn_kernel"); +}