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Subject[PATCH 1/6 v3] ptrace: Remove maxargs from task_current_syscall()
From: "Steven Rostedt (Red Hat)" <rostedt@goodmis.org>

task_current_syscall() has a single user that passes in 6 for maxargs, which
is the maximum arguments that can be used to get system calls from
syscall_get_arguments(). Instead of passing in a number of arguments to
grab, just get 6 arguments. The args argument even specifies that it's an
array of 6 items.

This will also allow changing syscall_get_arguments() to not get a variable
number of arguments, but always grab 6.

Linus also suggested not passing in a bunch of arguments to
task_current_syscall() but to instead pass in a pointer to a structure, and
just fill the structure. struct seccomp_data has almost all the parameters
that is needed except for the stack pointer (sp). As seccomp_data is part of
uapi, and I'm afraid to change it, a new structure was created
"syscall_info", which includes seccomp_data and adds the "sp" field.

Link: http://lkml.kernel.org/r/20161107213233.466776454@goodmis.org

Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Andy Lutomirski <luto@kernel.org>
Cc: Alexey Dobriyan <adobriyan@gmail.com>
Cc: Oleg Nesterov <oleg@redhat.com>
Cc: Kees Cook <keescook@chromium.org>
Cc: Al Viro <viro@zeniv.linux.org.uk>
Cc: linux-fsdevel@vger.kernel.org
Signed-off-by: Steven Rostedt (VMware) <rostedt@goodmis.org>
---
fs/proc/base.c | 17 +++++++------
include/linux/ptrace.h | 11 +++++---
lib/syscall.c | 57 ++++++++++++++++++------------------------
3 files changed, 42 insertions(+), 43 deletions(-)

diff --git a/fs/proc/base.c b/fs/proc/base.c
index ddef482f1334..6a803a0b75df 100644
--- a/fs/proc/base.c
+++ b/fs/proc/base.c
@@ -616,24 +616,25 @@ static int proc_pid_limits(struct seq_file *m, struct pid_namespace *ns,
static int proc_pid_syscall(struct seq_file *m, struct pid_namespace *ns,
struct pid *pid, struct task_struct *task)
{
- long nr;
- unsigned long args[6], sp, pc;
+ struct syscall_info info;
+ u64 *args = &info.data.args[0];
int res;

res = lock_trace(task);
if (res)
return res;

- if (task_current_syscall(task, &nr, args, 6, &sp, &pc))
+ if (task_current_syscall(task, &info))
seq_puts(m, "running\n");
- else if (nr < 0)
- seq_printf(m, "%ld 0x%lx 0x%lx\n", nr, sp, pc);
+ else if (info.data.nr < 0)
+ seq_printf(m, "%d 0x%llx 0x%llx\n",
+ info.data.nr, info.sp, info.data.instruction_pointer);
else
seq_printf(m,
- "%ld 0x%lx 0x%lx 0x%lx 0x%lx 0x%lx 0x%lx 0x%lx 0x%lx\n",
- nr,
+ "%d 0x%llx 0x%llx 0x%llx 0x%llx 0x%llx 0x%llx 0x%llx 0x%llx\n",
+ info.data.nr,
args[0], args[1], args[2], args[3], args[4], args[5],
- sp, pc);
+ info.sp, info.data.instruction_pointer);
unlock_trace(task);

return 0;
diff --git a/include/linux/ptrace.h b/include/linux/ptrace.h
index edb9b040c94c..d5084ebd9f03 100644
--- a/include/linux/ptrace.h
+++ b/include/linux/ptrace.h
@@ -9,6 +9,13 @@
#include <linux/bug.h> /* For BUG_ON. */
#include <linux/pid_namespace.h> /* For task_active_pid_ns. */
#include <uapi/linux/ptrace.h>
+#include <linux/seccomp.h>
+
+/* Add sp to seccomp_data, as seccomp is user API, we don't want to modify it */
+struct syscall_info {
+ __u64 sp;
+ struct seccomp_data data;
+};

extern int ptrace_access_vm(struct task_struct *tsk, unsigned long addr,
void *buf, int len, unsigned int gup_flags);
@@ -407,9 +414,7 @@ static inline void user_single_step_report(struct pt_regs *regs)
#define current_user_stack_pointer() user_stack_pointer(current_pt_regs())
#endif

-extern int task_current_syscall(struct task_struct *target, long *callno,
- unsigned long args[6], unsigned int maxargs,
- unsigned long *sp, unsigned long *pc);
+extern int task_current_syscall(struct task_struct *target, struct syscall_info *info);

extern void sigaction_compat_abi(struct k_sigaction *act, struct k_sigaction *oact);
#endif
diff --git a/lib/syscall.c b/lib/syscall.c
index 1a7077f20eae..e8467e17b9a2 100644
--- a/lib/syscall.c
+++ b/lib/syscall.c
@@ -5,16 +5,14 @@
#include <linux/export.h>
#include <asm/syscall.h>

-static int collect_syscall(struct task_struct *target, long *callno,
- unsigned long args[6], unsigned int maxargs,
- unsigned long *sp, unsigned long *pc)
+static int collect_syscall(struct task_struct *target, struct syscall_info *info)
{
struct pt_regs *regs;

if (!try_get_task_stack(target)) {
/* Task has no stack, so the task isn't in a syscall. */
- *sp = *pc = 0;
- *callno = -1;
+ memset(info, 0, sizeof(*info));
+ info->data.nr = -1;
return 0;
}

@@ -24,12 +22,13 @@ static int collect_syscall(struct task_struct *target, long *callno,
return -EAGAIN;
}

- *sp = user_stack_pointer(regs);
- *pc = instruction_pointer(regs);
+ info->sp = user_stack_pointer(regs);
+ info->data.instruction_pointer = instruction_pointer(regs);

- *callno = syscall_get_nr(target, regs);
- if (*callno != -1L && maxargs > 0)
- syscall_get_arguments(target, regs, 0, maxargs, args);
+ info->data.nr = syscall_get_nr(target, regs);
+ if (info->data.nr != -1L)
+ syscall_get_arguments(target, regs, 0, 6,
+ (unsigned long *)&info->data.args[0]);

put_task_stack(target);
return 0;
@@ -38,41 +37,35 @@ static int collect_syscall(struct task_struct *target, long *callno,
/**
* task_current_syscall - Discover what a blocked task is doing.
* @target: thread to examine
- * @callno: filled with system call number or -1
- * @args: filled with @maxargs system call arguments
- * @maxargs: number of elements in @args to fill
- * @sp: filled with user stack pointer
- * @pc: filled with user PC
+ * @info: structure with the following fields:
+ * .sp - filled with user stack pointer
+ * .data.nr - filled with system call number or -1
+ * .data.args - filled with @maxargs system call arguments
+ * .data.instruction_pointer - filled with user PC
*
- * If @target is blocked in a system call, returns zero with *@callno
- * set to the the call's number and @args filled in with its arguments.
- * Registers not used for system call arguments may not be available and
- * it is not kosher to use &struct user_regset calls while the system
+ * If @target is blocked in a system call, returns zero with @info.data.nr
+ * set to the the call's number and @info.data.args filled in with its
+ * arguments. Registers not used for system call arguments may not be available
+ * and it is not kosher to use &struct user_regset calls while the system
* call is still in progress. Note we may get this result if @target
* has finished its system call but not yet returned to user mode, such
* as when it's stopped for signal handling or syscall exit tracing.
*
* If @target is blocked in the kernel during a fault or exception,
- * returns zero with *@callno set to -1 and does not fill in @args.
- * If so, it's now safe to examine @target using &struct user_regset
- * get() calls as long as we're sure @target won't return to user mode.
+ * returns zero with *@info.data.nr set to -1 and does not fill in
+ * @info.data.args. If so, it's now safe to examine @target using
+ * &struct user_regset get() calls as long as we're sure @target won't return
+ * to user mode.
*
* Returns -%EAGAIN if @target does not remain blocked.
- *
- * Returns -%EINVAL if @maxargs is too large (maximum is six).
*/
-int task_current_syscall(struct task_struct *target, long *callno,
- unsigned long args[6], unsigned int maxargs,
- unsigned long *sp, unsigned long *pc)
+int task_current_syscall(struct task_struct *target, struct syscall_info *info)
{
long state;
unsigned long ncsw;

- if (unlikely(maxargs > 6))
- return -EINVAL;
-
if (target == current)
- return collect_syscall(target, callno, args, maxargs, sp, pc);
+ return collect_syscall(target, info);

state = target->state;
if (unlikely(!state))
@@ -80,7 +73,7 @@ int task_current_syscall(struct task_struct *target, long *callno,

ncsw = wait_task_inactive(target, state);
if (unlikely(!ncsw) ||
- unlikely(collect_syscall(target, callno, args, maxargs, sp, pc)) ||
+ unlikely(collect_syscall(target, info)) ||
unlikely(wait_task_inactive(target, state) != ncsw))
return -EAGAIN;

--
2.20.1

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