linux-kernel - [PATCH AUTOSEL 5.15 17/17] sh: sanitize the flags on sigreturn

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Date:   Sun, 19 Mar 2023 20:55:19 -0400
From:   Sasha Levin <sashal@...nel.org>
To:     linux-kernel@...r.kernel.org, stable@...r.kernel.org
Cc:     Al Viro <viro@...iv.linux.org.uk>, Rich Felker <dalias@...c.org>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        Sasha Levin <sashal@...nel.org>, ysato@...rs.sourceforge.jp,
        wangkefeng.wang@...wei.com, chenhuacai@...nel.org,
        catalin.marinas@....com, akpm@...ux-foundation.org,
        mpe@...erman.id.au, linux-sh@...r.kernel.org
Subject: [PATCH AUTOSEL 5.15 17/17] sh: sanitize the flags on sigreturn

From: Al Viro <viro@...iv.linux.org.uk>

[ Upstream commit 573b22ccb7ce9ab7f0539a2e11a9d3609a8783f5 ]

We fetch %SR value from sigframe; it might have been modified by signal
handler, so we can't trust it with any bits that are not modifiable in
user mode.

Signed-off-by: Al Viro <viro@...iv.linux.org.uk>
Cc: Rich Felker <dalias@...c.org>
Signed-off-by: Linus Torvalds <torvalds@...ux-foundation.org>
Signed-off-by: Sasha Levin <sashal@...nel.org>
---
 arch/sh/include/asm/processor_32.h | 1 +
 arch/sh/kernel/signal_32.c         | 3 +++
 2 files changed, 4 insertions(+)

diff --git a/arch/sh/include/asm/processor_32.h b/arch/sh/include/asm/processor_32.h
index aa92cc933889d..6c7966e627758 100644
--- a/arch/sh/include/asm/processor_32.h
+++ b/arch/sh/include/asm/processor_32.h
@@ -50,6 +50,7 @@
 #define SR_FD		0x00008000
 #define SR_MD		0x40000000
 
+#define SR_USER_MASK	0x00000303	// M, Q, S, T bits
 /*
  * DSP structure and data
  */
diff --git a/arch/sh/kernel/signal_32.c b/arch/sh/kernel/signal_32.c
index dd3092911efad..dc13702003f0f 100644
--- a/arch/sh/kernel/signal_32.c
+++ b/arch/sh/kernel/signal_32.c
@@ -115,6 +115,7 @@ static int
 restore_sigcontext(struct pt_regs *regs, struct sigcontext __user *sc, int *r0_p)
 {
 	unsigned int err = 0;
+	unsigned int sr = regs->sr & ~SR_USER_MASK;
 
 #define COPY(x)		err |= __get_user(regs->x, &sc->sc_##x)
 			COPY(regs[1]);
@@ -130,6 +131,8 @@ restore_sigcontext(struct pt_regs *regs, struct sigcontext __user *sc, int *r0_p
 	COPY(sr);	COPY(pc);
 #undef COPY
 
+	regs->sr = (regs->sr & SR_USER_MASK) | sr;
+
 #ifdef CONFIG_SH_FPU
 	if (boot_cpu_data.flags & CPU_HAS_FPU) {
 		int owned_fp;
-- 
2.39.2