[PATCH v3 3/6] ptrace: Order and comment PT_flags

Peter Zijlstra
2021-10-09T10:20:32Z

Add a comment to the PT_flags to indicate their actual value, this
makes it easier to see what bits are used and where there might be a
possible hole to use.

Notable PT_SEIZED was placed wrong, also PT_EVENT_FLAG() space seems
ill defined, as written is seems to be meant to cover the entire
PTRACE_O_ range offset by 3 bits, which would then be 3+[0..21],
however PT_SEIZED is in the middle of that.

XXX if at all possible, PT_SEIZED should be moved outside of this
range.

Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
---
include/linux/ptrace.h | 32 +++++++++++++++++---------------
include/uapi/linux/ptrace.h | 3 +++
2 files changed, 20 insertions(+), 15 deletions(-)

--- a/include/linux/ptrace.h
+++ b/include/linux/ptrace.h
@@ -28,30 +28,32 @@ extern int ptrace_access_vm(struct task_
* flags. When the a task is stopped the ptracer owns task->ptrace.
*/

-#define PT_SEIZED 0x00010000 /* SEIZE used, enable new behavior */
-#define PT_PTRACED 0x00000001
-#define PT_DTRACE 0x00000002 /* delayed trace (used on m68k, i386) */
+#define PT_PTRACED 0x00000001 // 0x00000001
+#define PT_DTRACE 0x00000002 /* delayed trace (used on m68k, i386) */ // 0x00000002

#define PT_OPT_FLAG_SHIFT 3
/* PT_TRACE_* event enable flags */
#define PT_EVENT_FLAG(event) (1 << (PT_OPT_FLAG_SHIFT + (event)))
-#define PT_TRACESYSGOOD PT_EVENT_FLAG(0)
-#define PT_TRACE_FORK PT_EVENT_FLAG(PTRACE_EVENT_FORK)
-#define PT_TRACE_VFORK PT_EVENT_FLAG(PTRACE_EVENT_VFORK)
-#define PT_TRACE_CLONE PT_EVENT_FLAG(PTRACE_EVENT_CLONE)
-#define PT_TRACE_EXEC PT_EVENT_FLAG(PTRACE_EVENT_EXEC)
-#define PT_TRACE_VFORK_DONE PT_EVENT_FLAG(PTRACE_EVENT_VFORK_DONE)
-#define PT_TRACE_EXIT PT_EVENT_FLAG(PTRACE_EVENT_EXIT)
-#define PT_TRACE_SECCOMP PT_EVENT_FLAG(PTRACE_EVENT_SECCOMP)

-#define PT_EXITKILL (PTRACE_O_EXITKILL << PT_OPT_FLAG_SHIFT)
-#define PT_SUSPEND_SECCOMP (PTRACE_O_SUSPEND_SECCOMP << PT_OPT_FLAG_SHIFT)
+#define PT_TRACESYSGOOD PT_EVENT_FLAG(0) // 0x00000008
+#define PT_TRACE_FORK PT_EVENT_FLAG(PTRACE_EVENT_FORK) // 0x00000010
+#define PT_TRACE_VFORK PT_EVENT_FLAG(PTRACE_EVENT_VFORK) // 0x00000020
+#define PT_TRACE_CLONE PT_EVENT_FLAG(PTRACE_EVENT_CLONE) // 0x00000040
+#define PT_TRACE_EXEC PT_EVENT_FLAG(PTRACE_EVENT_EXEC) // 0x00000080
+#define PT_TRACE_VFORK_DONE PT_EVENT_FLAG(PTRACE_EVENT_VFORK_DONE) // 0x00000100
+#define PT_TRACE_EXIT PT_EVENT_FLAG(PTRACE_EVENT_EXIT) // 0x00000200
+#define PT_TRACE_SECCOMP PT_EVENT_FLAG(PTRACE_EVENT_SECCOMP) // 0x00000400
+
+#define PT_SEIZED 0x00010000 /* SEIZE used, enable new behavior */// 0x00010000
+
+#define PT_EXITKILL (PTRACE_O_EXITKILL << PT_OPT_FLAG_SHIFT) // 0x00800000
+#define PT_SUSPEND_SECCOMP (PTRACE_O_SUSPEND_SECCOMP << PT_OPT_FLAG_SHIFT) // 0x01000000

/* single stepping state bits (used on ARM and PA-RISC) */
#define PT_SINGLESTEP_BIT 31
-#define PT_SINGLESTEP (1<<PT_SINGLESTEP_BIT)
+#define PT_SINGLESTEP (1<<PT_SINGLESTEP_BIT) // 0x80000000
#define PT_BLOCKSTEP_BIT 30
-#define PT_BLOCKSTEP (1<<PT_BLOCKSTEP_BIT)
+#define PT_BLOCKSTEP (1<<PT_BLOCKSTEP_BIT) // 0x40000000

extern long arch_ptrace(struct task_struct *child, long request,
unsigned long addr, unsigned long data);
--- a/include/uapi/linux/ptrace.h
+++ b/include/uapi/linux/ptrace.h
@@ -134,6 +134,7 @@ struct ptrace_rseq_configuration {
#define PTRACE_EVENT_STOP 128

/* Options set using PTRACE_SETOPTIONS or using PTRACE_SEIZE @data param */
+/* Consider overlap with task->ptrace PT_flags */
#define PTRACE_O_TRACESYSGOOD 1
#define PTRACE_O_TRACEFORK (1 << PTRACE_EVENT_FORK)
#define PTRACE_O_TRACEVFORK (1 << PTRACE_EVENT_VFORK)
@@ -143,6 +144,8 @@ struct ptrace_rseq_configuration {
#define PTRACE_O_TRACEEXIT (1 << PTRACE_EVENT_EXIT)
#define PTRACE_O_TRACESECCOMP (1 << PTRACE_EVENT_SECCOMP)

+/* PTRACE_O_SEIZED (1 << 13) */
+
/* eventless options */
#define PTRACE_O_EXITKILL (1 << 20)
#define PTRACE_O_SUSPEND_SECCOMP (1 << 21)