[PATCH] powerpc: Fix exit_flags field placement in pt_regs for ptrace

Commit d7a6797e0bc1 ("powerpc: add exit_flags field in pt_regs") added
the exit_flags field to struct pt_regs to pass internal exit control
flags (e.g. _TIF_RESTOREALL) from syscall_exit_prepare() to the
low-level assembly exit path.

However, the field was placed in a way that was visible to userspace
tools such as strace via PTRACE_GETREGS, or caused a struct layout or
size regression observable through ptrace. The field is purely
kernel-internal and must not be exposed beyond the user_pt_regs
boundary.

Move exit_flags into struct thread_info where it is only accessible to
the kernel, and keep it out of the ptrace-visible register window
entirely.

Fixes: d7a6797e0bc1 ("powerpc: add exit_flags field in pt_regs")
Reported-by: "Dmitry V. Levin" <[email protected]>
Closes: https://lore.kernel.org/all/[email protected]/
Signed-off-by: Mukesh Kumar Chaurasiya (IBM) <[email protected]>
---
 arch/powerpc/include/asm/ptrace.h      |  3 ---
 arch/powerpc/include/asm/thread_info.h |  1 +
 arch/powerpc/include/uapi/asm/ptrace.h | 14 ++++-------
 arch/powerpc/kernel/interrupt.c        | 32 +++++++++++++++-----------
 arch/powerpc/kernel/ptrace/ptrace.c    |  1 -
 arch/powerpc/kernel/signal.c           |  2 +-
 6 files changed, 26 insertions(+), 27 deletions(-)

diff --git a/arch/powerpc/include/asm/ptrace.h b/arch/powerpc/include/asm/ptrace.h
index fdeb97421785..d53c4dd4d8b6 100644
--- a/arch/powerpc/include/asm/ptrace.h
+++ b/arch/powerpc/include/asm/ptrace.h
@@ -53,9 +53,6 @@ struct pt_regs
 				unsigned long esr;
 			};
 			unsigned long result;
-			unsigned long exit_flags;
-			/* Maintain 16 byte interrupt stack alignment */
-			unsigned long __pt_regs_pad[3];
 		};
 	};
 #if defined(CONFIG_PPC64) || defined(CONFIG_PPC_KUAP)
diff --git a/arch/powerpc/include/asm/thread_info.h b/arch/powerpc/include/asm/thread_info.h
index ee3b9adb5b67..0487e94d3416 100644
--- a/arch/powerpc/include/asm/thread_info.h
+++ b/arch/powerpc/include/asm/thread_info.h
@@ -57,6 +57,7 @@ struct thread_info {
 #ifdef CONFIG_SMP
 	unsigned int	cpu;
 #endif
+	unsigned long	exit_flags;		/* Exit Flags for entry/exit */
 	unsigned long	syscall_work;		/* SYSCALL_WORK_ flags */
 	unsigned long	local_flags;		/* private flags for thread */
 #ifdef CONFIG_LIVEPATCH_64
diff --git a/arch/powerpc/include/uapi/asm/ptrace.h b/arch/powerpc/include/uapi/asm/ptrace.h
index a393b7f2760a..01e630149d48 100644
--- a/arch/powerpc/include/uapi/asm/ptrace.h
+++ b/arch/powerpc/include/uapi/asm/ptrace.h
@@ -55,8 +55,6 @@ struct pt_regs
 	unsigned long dar;		/* Fault registers */
 	unsigned long dsisr;		/* on 4xx/Book-E used for ESR */
 	unsigned long result;		/* Result of a system call */
-	unsigned long exit_flags;	/* System call exit flags */
-	unsigned long __pt_regs_pad[3];	/* Maintain 16 byte interrupt stack alignment */
 };
 
 #endif /* __ASSEMBLER__ */
@@ -116,12 +114,10 @@ struct pt_regs
 #define PT_DAR	41
 #define PT_DSISR 42
 #define PT_RESULT 43
-#define PT_EXIT_FLAGS 44
-#define PT_PAD 47 /* 3 times */
-#define PT_DSCR 48
-#define PT_REGS_COUNT 48
+#define PT_DSCR 44
+#define PT_REGS_COUNT 44
 
-#define PT_FPR0	(PT_REGS_COUNT + 4)	/* each FP reg occupies 2 slots in this space */
+#define PT_FPR0	48	/* each FP reg occupies 2 slots in this space */
 
 #ifndef __powerpc64__
 
@@ -133,7 +129,7 @@ struct pt_regs
 #define PT_FPSCR (PT_FPR0 + 32)	/* each FP reg occupies 1 slot in 64-bit space */
 
 
-#define PT_VR0	(PT_FPSCR + 2)	/* <82> each Vector reg occupies 2 slots in 64-bit */
+#define PT_VR0 82	/* each Vector reg occupies 2 slots in 64-bit */
 #define PT_VSCR (PT_VR0 + 32*2 + 1)
 #define PT_VRSAVE (PT_VR0 + 33*2)
 
@@ -141,7 +137,7 @@ struct pt_regs
 /*
  * Only store first 32 VSRs here. The second 32 VSRs in VR0-31
  */
-#define PT_VSR0	(PT_VRSAVE + 2)	/* each VSR reg occupies 2 slots in 64-bit */
+#define PT_VSR0 150	/* each VSR reg occupies 2 slots in 64-bit */
 #define PT_VSR31 (PT_VSR0 + 2*31)
 #endif /* __powerpc64__ */
 
diff --git a/arch/powerpc/kernel/interrupt.c b/arch/powerpc/kernel/interrupt.c
index f04978080837..5b88bf72786c 100644
--- a/arch/powerpc/kernel/interrupt.c
+++ b/arch/powerpc/kernel/interrupt.c
@@ -89,15 +89,17 @@ notrace unsigned long syscall_exit_prepare(unsigned long r3,
 					   long scv)
 {
 	unsigned long ti_flags;
+	unsigned long ret = 0;
 	bool is_not_scv = !IS_ENABLED(CONFIG_PPC_BOOK3S_64) || !scv;
 
 	kuap_assert_locked();
 
 	regs->result = r3;
-	regs->exit_flags = 0;
 
-	ti_flags = read_thread_flags();
+	/* Clear exit_flags so only flags set during this exit are visible */
+	current->thread_info.exit_flags = 0;
 
+	ti_flags = read_thread_flags();
 	if (unlikely(r3 >= (unsigned long)-MAX_ERRNO) && is_not_scv) {
 		if (likely(!(ti_flags & (_TIF_NOERROR | _TIF_RESTOREALL)))) {
 			r3 = -r3;
@@ -107,7 +109,7 @@ notrace unsigned long syscall_exit_prepare(unsigned long r3,
 
 	if (unlikely(ti_flags & _TIF_PERSYSCALL_MASK)) {
 		if (ti_flags & _TIF_RESTOREALL)
-			regs->exit_flags = _TIF_RESTOREALL;
+			ret = _TIF_RESTOREALL;
 		else
 			regs->gpr[3] = r3;
 		clear_bits(_TIF_PERSYSCALL_MASK, &current_thread_info()->flags);
@@ -116,7 +118,7 @@ notrace unsigned long syscall_exit_prepare(unsigned long r3,
 	}
 
 	if (unlikely(ti_flags & _TIF_SYSCALL_DOTRACE)) {
-		regs->exit_flags |= _TIF_RESTOREALL;
+		ret |= _TIF_RESTOREALL;
 	}
 
 	syscall_exit_to_user_mode(regs);
@@ -132,17 +134,19 @@ notrace unsigned long syscall_exit_prepare(unsigned long r3,
 
 	/* Restore user access locks last */
 	kuap_user_restore(regs);
-
+	ret |= current->thread_info.exit_flags;
 #ifdef CONFIG_PPC64
-	regs->exit_result = regs->exit_flags;
+	regs->exit_result = ret;
 #endif
 
-	return regs->exit_flags;
+	return ret;
 }
 
 #ifdef CONFIG_PPC64
 notrace unsigned long syscall_exit_restart(unsigned long r3, struct pt_regs *regs)
 {
+	unsigned long ret;
+
 	/*
 	 * This is called when detecting a soft-pending interrupt as well as
 	 * an alternate-return interrupt. So we can't just have the alternate
@@ -167,9 +171,11 @@ notrace unsigned long syscall_exit_restart(unsigned long r3, struct pt_regs *reg
 	}
 
 	kuap_user_restore(regs);
-	regs->exit_result |= regs->exit_flags;
+	ret = current_thread_info()->exit_flags & _TIF_RESTOREALL;
+	current_thread_info()->exit_flags &= ~_TIF_RESTOREALL;
+	regs->exit_result |= ret;
 
-	return regs->exit_result;
+	return ret;
 }
 #endif
 
@@ -186,8 +192,10 @@ notrace unsigned long interrupt_exit_user_prepare(struct pt_regs *regs)
 	 */
 	kuap_assert_locked();
 
+	/* Clear exit_flags so only flags set during this exit are visible */
+	current_thread_info()->exit_flags = 0;
+
 	local_irq_disable();
-	regs->exit_flags = 0;
 again:
 	check_return_regs_valid(regs);
 	user_enter_irqoff();
@@ -200,9 +208,7 @@ notrace unsigned long interrupt_exit_user_prepare(struct pt_regs *regs)
 
 	/* Restore user access locks last */
 	kuap_user_restore(regs);
-
-	ret = regs->exit_flags;
-
+	ret = current_thread_info()->exit_flags & _TIF_RESTOREALL;
 #ifdef CONFIG_PPC64
 	regs->exit_result = ret;
 #endif
diff --git a/arch/powerpc/kernel/ptrace/ptrace.c b/arch/powerpc/kernel/ptrace/ptrace.c
index 316d4f5ead8e..6cd180bc36ab 100644
--- a/arch/powerpc/kernel/ptrace/ptrace.c
+++ b/arch/powerpc/kernel/ptrace/ptrace.c
@@ -291,7 +291,6 @@ void __init pt_regs_check(void)
 	CHECK_REG(PT_DAR, dar);
 	CHECK_REG(PT_DSISR, dsisr);
 	CHECK_REG(PT_RESULT, result);
-	CHECK_REG(PT_EXIT_FLAGS, exit_flags);
 	#undef CHECK_REG
 
 	BUILD_BUG_ON(PT_REGS_COUNT != sizeof(struct user_pt_regs) / sizeof(unsigned long));
diff --git a/arch/powerpc/kernel/signal.c b/arch/powerpc/kernel/signal.c
index bb42a8b6c642..cc6498501610 100644
--- a/arch/powerpc/kernel/signal.c
+++ b/arch/powerpc/kernel/signal.c
@@ -356,6 +356,6 @@ void signal_fault(struct task_struct *tsk, struct pt_regs *regs,
 void arch_do_signal_or_restart(struct pt_regs *regs)
 {
 	BUG_ON(regs != current->thread.regs);
-	regs->exit_flags |= _TIF_RESTOREALL;
+	current_thread_info()->exit_flags |= _TIF_RESTOREALL;
 	do_signal(current);
 }
-- 
2.55.0