Re: [PATCH v4 2/2] selftests/vm/pkeys: Add a regression test for setting PKRU through ptrace

Ingo Molnar
2022-08-06T08:52:37Z

* Kyle Huey <me@kylehuey.com> wrote:

> From: Kyle Huey <me@kylehuey.com>
>
> This tests PTRACE_SETREGSET with NT_X86_XSTATE modifying PKRU directly and
> removing the PKRU bit from XSTATE_BV.
>
> Signed-off-by: Kyle Huey <me@kylehuey.com>
> ---
> tools/testing/selftests/vm/pkey-x86.h | 12 +++
> tools/testing/selftests/vm/protection_keys.c | 88 +++++++++++++++++++-
> 2 files changed, 98 insertions(+), 2 deletions(-)
>
> diff --git a/tools/testing/selftests/vm/pkey-x86.h b/tools/testing/selftests/vm/pkey-x86.h
> index b078ce9c6d2a..72c14cd3ddc7 100644
> --- a/tools/testing/selftests/vm/pkey-x86.h
> +++ b/tools/testing/selftests/vm/pkey-x86.h
> @@ -104,6 +104,18 @@ static inline int cpu_has_pkeys(void)
> return 1;
> }
>
> +static inline int cpu_max_xsave_size(void)
> +{
> + unsigned long XSTATE_CPUID = 0xd;
> + unsigned int eax;
> + unsigned int ebx;
> + unsigned int ecx;
> + unsigned int edx;
> +
> + __cpuid_count(XSTATE_CPUID, 0, eax, ebx, ecx, edx);
> + return ecx;
> +}
> +
> static inline u32 pkey_bit_position(int pkey)
> {
> return pkey * PKEY_BITS_PER_PKEY;
> diff --git a/tools/testing/selftests/vm/protection_keys.c b/tools/testing/selftests/vm/protection_keys.c
> index 291bc1e07842..27759d3ed9cd 100644
> --- a/tools/testing/selftests/vm/protection_keys.c
> +++ b/tools/testing/selftests/vm/protection_keys.c
> @@ -18,12 +18,13 @@
> * do a plain mprotect() to a mprotect_pkey() area and make sure the pkey sticks
> *
> * Compile like this:
> - * gcc -o protection_keys -O2 -g -std=gnu99 -pthread -Wall protection_keys.c -lrt -ldl -lm
> - * gcc -m32 -o protection_keys_32 -O2 -g -std=gnu99 -pthread -Wall protection_keys.c -lrt -ldl -lm
> + * gcc -mxsave -o protection_keys -O2 -g -std=gnu99 -pthread -Wall protection_keys.c -lrt -ldl -lm
> + * gcc -mxsave -m32 -o protection_keys_32 -O2 -g -std=gnu99 -pthread -Wall protection_keys.c -lrt -ldl -lm
> */
> #define _GNU_SOURCE
> #define __SANE_USERSPACE_TYPES__
> #include <errno.h>
> +#include <linux/elf.h>
> #include <linux/futex.h>
> #include <time.h>
> #include <sys/time.h>
> @@ -1550,6 +1551,86 @@ void test_implicit_mprotect_exec_only_memory(int *ptr, u16 pkey)
> do_not_expect_pkey_fault("plain read on recently PROT_EXEC area");
> }
>
> +#if defined(__i386__) || defined(__x86_64__)
> +void test_ptrace_modifies_pkru(int *ptr, u16 pkey)
> +{
> + pid_t child;
> + int status, ret;
> + int pkey_offset = pkey_reg_xstate_offset();
> + size_t xsave_size = cpu_max_xsave_size();
> + void *xsave;
> + u32 *pkey_register;
> + u64 *xstate_bv;
> + struct iovec iov;
> +
> + child = fork();
> + pkey_assert(child >= 0);
> + dprintf3("[%d] fork() ret: %d\n", getpid(), child);
> + if (!child) {
> + u32 pkey_register = read_pkey_reg();
> +
> + ptrace(PTRACE_TRACEME, 0, 0, 0);
> + raise(SIGSTOP);
> +
> + /*
> + * need __read_pkey_reg() version so we do not do shadow_pkey_reg
> + * checking
> + */
> + if (pkey_register == __read_pkey_reg())
> + exit(1);
> +
> + raise(SIGSTOP);
> +
> + exit(__read_pkey_reg());
> + }
> +
> + pkey_assert(child == waitpid(child, &status, 0));
> + dprintf3("[%d] waitpid(%d) status: %x\n", getpid(), child, status);
> + pkey_assert(WIFSTOPPED(status) && WSTOPSIG(status) == SIGSTOP);
> +
> + xsave = (void *)malloc(xsave_size);
> + pkey_assert(xsave > 0);
> +
> + iov.iov_base = xsave;
> + iov.iov_len = xsave_size;
> + ret = ptrace(PTRACE_GETREGSET, child, (void *)NT_X86_XSTATE, &iov);
> + pkey_assert(ret == 0);
> +
> + pkey_register = (u32 *)(xsave + pkey_offset);
> + pkey_assert(*pkey_register == read_pkey_reg());
> +
> + *pkey_register = !read_pkey_reg();
> +
> + ret = ptrace(PTRACE_SETREGSET, child, (void *)NT_X86_XSTATE, &iov);
> + pkey_assert(ret == 0);
> +
> + ret = ptrace(PTRACE_CONT, child, 0, 0);
> + pkey_assert(ret == 0);
> +
> + pkey_assert(child == waitpid(child, &status, 0));
> + dprintf3("[%d] waitpid(%d) status: %x\n", getpid(), child, status);
> + pkey_assert(WIFSTOPPED(status) && WSTOPSIG(status) == SIGSTOP);
> +
> + ret = ptrace(PTRACE_GETREGSET, child, (void *)NT_X86_XSTATE, &iov);
> + pkey_assert(ret == 0);
> +
> + xstate_bv = (u64 *)(xsave + 512);
> + *xstate_bv &= ~(1 << 9);
> +
> + ret = ptrace(PTRACE_SETREGSET, child, (void *)NT_X86_XSTATE, &iov);
> + pkey_assert(ret == 0);
> +
> + ret = ptrace(PTRACE_CONT, child, 0, 0);
> + pkey_assert(ret == 0);
> +
> + pkey_assert(child == waitpid(child, &status, 0));
> + dprintf3("[%d] waitpid(%d) status: %x\n", getpid(), child, status);
> + pkey_assert(WIFEXITED(status));
> + pkey_assert(WEXITSTATUS(status) == 0);
> + free(xsave);

LGTM.

May I ask for a bit more in terms of testing the ABI: writing some
non-trivial (not all-zero and not all-ones) value into the PKRU register,
forcing the child task to go through a FPU save/restore context switch
and then reading it back and verifying the value, or something like that?

Thanks,

Ingo