riscv: Fix register corruption from uninitialized cregs on error

[ Upstream commit 6ebcbb5 ]

compat_riscv_gpr_set() calls cregs_to_regs() unconditionally, even when
user_regset_copyin() fails. Since cregs is an uninitialized stack
variable, a copyin failure causes uninitialized stack data to be written
into the target task's pt_regs, corrupting its register state and
potentially leaking kernel stack contents.

compat_restore_sigcontext() has the same issue: it calls cregs_to_regs()
even when __copy_from_user() fails, leading to the same corruption of
the signal-returning task's register state on error.

Only call cregs_to_regs() when the user copy succeeds.

Fixes: 4608c15 ("riscv: compat: ptrace: Add compat_arch_ptrace implement")
Fixes: 7383ee0 ("riscv: compat: signal: Add rt_frame implementation")
Signed-off-by: Michael Neuling <mikey@neuling.org>
Assisted-by: Cursor:claude-4.6-opus-high-thinking
Link: https://patch.msgid.link/20260501062320.2339562-1-mikey@neuling.org
Signed-off-by: Paul Walmsley <pjw@kernel.org>
Signed-off-by: Sasha Levin <sashal@kernel.org>

Author: mikey

arch/riscv/kernel/compat_signal.c

@@ -107,6 +107,8 @@ static long compat_restore_sigcontext(struct pt_regs *regs,
 
 	/* sc_regs is structured the same as the start of pt_regs */
 	err = __copy_from_user(&cregs, &sc->sc_regs, sizeof(sc->sc_regs));
+	if (unlikely(err))
+		return err;
 
 	cregs_to_regs(&cregs, regs);
 

arch/riscv/kernel/ptrace.c

@@ -291,8 +291,8 @@ static int compat_riscv_gpr_set(struct task_struct *target,
 	struct compat_user_regs_struct cregs;
 
 	ret = user_regset_copyin(&pos, &count, &kbuf, &ubuf, &cregs, 0, -1);
-
-	cregs_to_regs(&cregs, task_pt_regs(target));
+	if (!ret)
+		cregs_to_regs(&cregs, task_pt_regs(target));
 
 	return ret;
 }