Re: [PATCH v2 2/2] riscv: selftests: Add a ptrace test to verify syscall parameter modification

[Charlie Jenkins <charlie@rivosinc.com>]

On Fri, Dec 20, 2024 at 05:29:45AM +0800, Celeste Liu wrote:
> 
> On 2024-12-20 02:26, Charlie Jenkins wrote:
> > On Tue, Dec 03, 2024 at 01:55:07PM +0100, Andrew Jones wrote:
> >> On Tue, Dec 03, 2024 at 05:30:05PM +0800, Celeste Liu wrote:
> >>> From: Charlie Jenkins <charlie@rivosinc.com>
> >>>
> >>> This test checks that orig_a0 allows a syscall argument to be modified,
> >>> and that changing a0 does not change the syscall argument.
> >>>
> >>> Cc: stable@vger.kernel.org
> >>> Co-developed-by: Quan Zhou <zhouquan@iscas.ac.cn>
> >>> Signed-off-by: Quan Zhou <zhouquan@iscas.ac.cn>
> >>> Co-developed-by: Celeste Liu <uwu@coelacanthus.name>
> >>> Signed-off-by: Celeste Liu <uwu@coelacanthus.name>
> >>> Signed-off-by: Charlie Jenkins <charlie@rivosinc.com>
> >>> ---
> >>>  tools/testing/selftests/riscv/abi/.gitignore |   1 +
> >>>  tools/testing/selftests/riscv/abi/Makefile   |   5 +-
> >>>  tools/testing/selftests/riscv/abi/ptrace.c   | 134 +++++++++++++++++++++++++++
> >>>  3 files changed, 139 insertions(+), 1 deletion(-)
> >>>
> >>> diff --git a/tools/testing/selftests/riscv/abi/.gitignore b/tools/testing/selftests/riscv/abi/.gitignore
> >>> index b38358f91c4d2240ae64892871d9ca98bda1ae58..378c605919a3b3d58eec2701eb7af430cfe315d6 100644
> >>> --- a/tools/testing/selftests/riscv/abi/.gitignore
> >>> +++ b/tools/testing/selftests/riscv/abi/.gitignore
> >>> @@ -1 +1,2 @@
> >>>  pointer_masking
> >>> +ptrace
> >>> diff --git a/tools/testing/selftests/riscv/abi/Makefile b/tools/testing/selftests/riscv/abi/Makefile
> >>> index ed82ff9c664e7eb3f760cbab81fb957ff72579c5..3f74d059dfdcbce4d45d8ff618781ccea1419061 100644
> >>> --- a/tools/testing/selftests/riscv/abi/Makefile
> >>> +++ b/tools/testing/selftests/riscv/abi/Makefile
> >>> @@ -2,9 +2,12 @@
> >>>  
> >>>  CFLAGS += -I$(top_srcdir)/tools/include
> >>>  
> >>> -TEST_GEN_PROGS := pointer_masking
> >>> +TEST_GEN_PROGS := pointer_masking ptrace
> >>>  
> >>>  include ../../lib.mk
> >>>  
> >>>  $(OUTPUT)/pointer_masking: pointer_masking.c
> >>>  	$(CC) -static -o$@ $(CFLAGS) $(LDFLAGS) $^
> >>> +
> >>> +$(OUTPUT)/ptrace: ptrace.c
> >>> +	$(CC) -static -o$@ $(CFLAGS) $(LDFLAGS) $^
> >>> diff --git a/tools/testing/selftests/riscv/abi/ptrace.c b/tools/testing/selftests/riscv/abi/ptrace.c
> >>> new file mode 100644
> >>> index 0000000000000000000000000000000000000000..d192764b428d1f1c442f3957c6fedeb01a48d556
> >>> --- /dev/null
> >>> +++ b/tools/testing/selftests/riscv/abi/ptrace.c
> >>> @@ -0,0 +1,134 @@
> >>> +// SPDX-License-Identifier: GPL-2.0-only
> >>> +#include <stdio.h>
> >>> +#include <stdlib.h>
> >>> +#include <string.h>
> >>> +#include <unistd.h>
> >>> +#include <fcntl.h>
> >>> +#include <signal.h>
> >>> +#include <errno.h>
> >>> +#include <sys/types.h>
> >>> +#include <sys/ptrace.h>
> >>> +#include <sys/stat.h>
> >>> +#include <sys/user.h>
> >>> +#include <sys/wait.h>
> >>> +#include <sys/uio.h>
> >>> +#include <linux/elf.h>
> >>> +#include <linux/unistd.h>
> >>> +#include <asm/ptrace.h>
> >>> +
> >>> +#include "../../kselftest_harness.h"
> >>> +
> >>> +#define ORIG_A0_MODIFY      0x01
> >>> +#define A0_MODIFY           0x02
> >>> +#define A0_OLD              0x03
> >>> +#define A0_NEW              0x04
> >>
> >> Shouldn't A0_OLD and A0_NEW set more bits, since 3 and 4 aren't very
> >> unique (we could have those values by accident)? And should we include
> >> setting bits over 31 for 64-bit targets?
> >>
> >>> +
> >>> +#define perr_and_exit(fmt, ...)						\
> >>> +	({								\
> >>> +		char buf[256];						\
> >>> +		snprintf(buf, sizeof(buf), "%s:%d:" fmt ": %m\n",	\
> >>> +			__func__, __LINE__, ##__VA_ARGS__);		\
> >>> +		perror(buf);						\
> >>> +		exit(-1);						\
> >>> +	})
> >>
> >> Can we use e.g. ksft_exit_fail_perror() instead? I'd prefer we try to
> >> consolidate testing/selftests/riscv/* tests on a common format for
> >> errors and exit codes and we're already using other kselftest stuff.
> >>
> >>> +
> >>> +static inline void resume_and_wait_tracee(pid_t pid, int flag)
> >>> +{
> >>> +	int status;
> >>> +
> >>> +	if (ptrace(flag, pid, 0, 0))
> >>> +		perr_and_exit("failed to resume the tracee %d\n", pid);
> >>> +
> >>> +	if (waitpid(pid, &status, 0) != pid)
> >>> +		perr_and_exit("failed to wait for the tracee %d\n", pid);
> >>> +}
> >>> +
> >>> +static void ptrace_test(int opt, int *result)
> >>> +{
> >>> +	int status;
> >>> +	pid_t pid;
> >>> +	struct user_regs_struct regs;
> >>> +	struct iovec iov = {
> >>> +		.iov_base = &regs,
> >>> +		.iov_len = sizeof(regs),
> >>> +	};
> >>> +
> >>> +	unsigned long orig_a0;
> >>> +	struct iovec a0_iov = {
> >>> +		.iov_base = &orig_a0,
> >>> +		.iov_len = sizeof(orig_a0),
> >>> +	};
> >>> +
> >>> +	pid = fork();
> >>> +	if (pid == 0) {
> >>> +		/* Mark oneself being traced */
> >>> +		long val = ptrace(PTRACE_TRACEME, 0, 0, 0);
> >>> +
> >>> +		if (val)
> >>> +			perr_and_exit("failed to request for tracer to trace me: %ld\n", val);
> >>> +
> >>> +		kill(getpid(), SIGSTOP);
> >>> +
> >>> +		/* Perform exit syscall that will be intercepted */
> >>> +		exit(A0_OLD);
> >>> +	}
> >>> +
> >>> +	if (pid < 0)
> >>> +		exit(1);
> >>
> >> This unexpected error condition deserves a message, so I'd use
> >> ksft_exit_fail_perror() here.
> >>
> >>> +
> >>> +	if (waitpid(pid, &status, 0) != pid)
> >>> +		perr_and_exit("failed to wait for the tracee %d\n", pid);
> >>> +
> >>> +	/* Stop at the entry point of the syscall */
> >>> +	resume_and_wait_tracee(pid, PTRACE_SYSCALL);
> >>> +
> >>> +	/* Check tracee regs before the syscall */
> >>> +	if (ptrace(PTRACE_GETREGSET, pid, NT_PRSTATUS, &iov))
> >>> +		perr_and_exit("failed to get tracee registers\n");
> >>> +	if (ptrace(PTRACE_GETREGSET, pid, NT_RISCV_ORIG_A0, &a0_iov))
> >>> +		perr_and_exit("failed to get tracee registers\n");
> >>> +	if (orig_a0 != A0_OLD)
> >>> +		perr_and_exit("unexpected orig_a0: 0x%lx\n", orig_a0);
> >>> +
> >>> +	/* Modify a0/orig_a0 for the syscall */
> >>> +	switch (opt) {
> >>> +	case A0_MODIFY:
> >>> +		regs.a0 = A0_NEW;
> >>> +		break;
> >>> +	case ORIG_A0_MODIFY:
> >>> +		orig_a0 = A0_NEW;
> >>> +		break;
> >>> +	}
> >>> +
> >>> +	if (ptrace(PTRACE_SETREGSET, pid, NT_RISCV_ORIG_A0, &a0_iov))
> >>> +		perr_and_exit("failed to set tracee registers\n");
> >>> +
> >>> +	/* Resume the tracee */
> >>> +	ptrace(PTRACE_CONT, pid, 0, 0);
> >>> +	if (waitpid(pid, &status, 0) != pid)
> >>> +		perr_and_exit("failed to wait for the tracee\n");
> >>> +
> >>> +	*result = WEXITSTATUS(status);
> >>> +}
> >>> +
> >>> +TEST(ptrace_modify_a0)
> >>> +{
> >>> +	int result;
> >>> +
> >>> +	ptrace_test(A0_MODIFY, &result);
> >>> +
> >>> +	/* The modification of a0 cannot affect the first argument of the syscall */
> >>> +	EXPECT_EQ(A0_OLD, result);
> >>
> >> What about checking that we actually set regs.a0 to A0_NEW? We'd need
> >> A0_NEW to be more unique than 4, though.
> >>
> >>> +}
> >>> +
> >>> +TEST(ptrace_modify_orig_a0)
> >>> +{
> >>> +	int result;
> >>> +
> >>> +	ptrace_test(ORIG_A0_MODIFY, &result);
> >>> +
> >>> +	/* Only modify orig_a0 to change the first argument of the syscall */
> >>
> >> If we run ptrace_modify_a0 first then we've already set regs.a0 to A0_NEW
> >> and can't check with this test that we don't set it to A0_NEW. We should
> >> probably have two different test values, one for regs.a0 and one for
> >> orig_a0 and ensure on both tests that we aren't writing both.
> >>
> > 
> > Celeste, do you want to fix this up or are you waiting for me to?
> 
> Sorry for delay. I was busy with household affairs in the past few weeks.
> v3 will be sent tomorrow or the day after tomorrow.
> 
> I am deeply sorry for this.

No need to apologize! Just wanted to make sure you weren't expected me
to update the test :)

- Charlie

> 
> > 
> > - Charlie
> > 
> >>> +	EXPECT_EQ(A0_NEW, result);
> >>> +}
> >>> +
> >>> +TEST_HARNESS_MAIN
> >>>
> >>> -- 
> >>> 2.47.0
> >>>
> >>
> >> Thanks,
> >> drew
>