[PATCH] riscv: fix out of bounds in walk_stackframe

[Edward AD]

Increase the check on the frame after assigning its value. This is to prevent 
frame access from crossing boundaries.

Closes: https://lore.kernel.org/all/20230926105949.1025995-2-twuufnxlz@gmail.com/
Fixes: 5d8544e2d007 ("RISC-V: Generic library routines and assembly")
Reported-and-tested-by: syzbot+8d2757d62d403b2d9275 at syzkaller.appspotmail.com
Link: https://lore.kernel.org/all/0000000000000170df0605ccf91a@google.com/T/
Signed-off-by: Edward AD <twuufnxlz at gmail.com>
---
 arch/riscv/kernel/stacktrace.c | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/arch/riscv/kernel/stacktrace.c b/arch/riscv/kernel/stacktrace.c
index 64a9c093aef9..53bd18672329 100644
--- a/arch/riscv/kernel/stacktrace.c
+++ b/arch/riscv/kernel/stacktrace.c
@@ -54,6 +54,8 @@ void notrace walk_stackframe(struct task_struct *task, struct pt_regs *regs,
 			break;
 		/* Unwind stack frame */
 		frame = (struct stackframe *)fp - 1;
+		if (!virt_addr_valid(frame))
+			break;
 		sp = fp;
 		if (regs && (regs->epc == pc) && (frame->fp & 0x7)) {
 			fp = frame->ra;
-- 
2.25.1