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

* 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