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Message-ID: <Z2RlR1cP9tne8rNi@ghost>
Date: Thu, 19 Dec 2024 10:26:15 -0800
From: Charlie Jenkins <charlie@...osinc.com>
To: Andrew Jones <ajones@...tanamicro.com>
Cc: Celeste Liu <uwu@...lacanthus.name>, Oleg Nesterov <oleg@...hat.com>,
Paul Walmsley <paul.walmsley@...ive.com>,
Palmer Dabbelt <palmer@...belt.com>,
Albert Ou <aou@...s.berkeley.edu>,
Eric Biederman <ebiederm@...ssion.com>, Kees Cook <kees@...nel.org>,
Shuah Khan <shuah@...nel.org>, Alexandre Ghiti <alex@...ti.fr>,
"Dmitry V. Levin" <ldv@...ace.io>,
Andrea Bolognani <abologna@...hat.com>,
Björn Töpel <bjorn@...nel.org>,
Thomas Gleixner <tglx@...utronix.de>, Ron Economos <re@...z.net>,
Quan Zhou <zhouquan@...as.ac.cn>,
Felix Yan <felixonmars@...hlinux.org>,
Ruizhe Pan <c141028@...il.com>,
Shiqi Zhang <shiqi@...c.iscas.ac.cn>, Guo Ren <guoren@...nel.org>,
Yao Zi <ziyao@...root.org>, Han Gao <gaohan@...as.ac.cn>,
linux-riscv@...ts.infradead.org, linux-kernel@...r.kernel.org,
linux-mm@...ck.org, stable@...r.kernel.org,
linux-kselftest@...r.kernel.org
Subject: Re: [PATCH v2 2/2] riscv: selftests: Add a ptrace test to verify
syscall parameter modification
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@...osinc.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@...r.kernel.org
> > Co-developed-by: Quan Zhou <zhouquan@...as.ac.cn>
> > Signed-off-by: Quan Zhou <zhouquan@...as.ac.cn>
> > Co-developed-by: Celeste Liu <uwu@...lacanthus.name>
> > Signed-off-by: Celeste Liu <uwu@...lacanthus.name>
> > Signed-off-by: Charlie Jenkins <charlie@...osinc.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 = ®s,
> > + .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?
- Charlie
> > + EXPECT_EQ(A0_NEW, result);
> > +}
> > +
> > +TEST_HARNESS_MAIN
> >
> > --
> > 2.47.0
> >
>
> Thanks,
> drew
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