linux-kernel - [PATCH v4 7/8] arm64: Forbid calling compat sigreturn from 64-bit tasks

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Message-Id: <20210430203757.47653-6-amanieu@gmail.com>
Date:   Fri, 30 Apr 2021 21:37:56 +0100
From:   Amanieu d'Antras <amanieu@...il.com>
To:     unlisted-recipients:; (no To-header on input)
Cc:     Amanieu d'Antras <amanieu@...il.com>,
        Ryan Houdek <Houdek.Ryan@...-emu.org>,
        Catalin Marinas <catalin.marinas@....com>,
        Will Deacon <will@...nel.org>,
        Mark Rutland <mark.rutland@....com>,
        Steven Price <steven.price@....com>,
        Arnd Bergmann <arnd@...nel.org>,
        David Laight <David.Laight@...lab.com>,
        Mark Brown <broonie@...nel.org>,
        linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org
Subject: [PATCH v4 7/8] arm64: Forbid calling compat sigreturn from 64-bit tasks

It's impossible for this syscall to do anything sensible in this
context.

Signed-off-by: Amanieu d'Antras <amanieu@...il.com>
Co-developed-by: Ryan Houdek <Houdek.Ryan@...-emu.org>
Signed-off-by: Ryan Houdek <Houdek.Ryan@...-emu.org>
---
 arch/arm64/kernel/signal32.c | 8 ++++++++
 1 file changed, 8 insertions(+)

diff --git a/arch/arm64/kernel/signal32.c b/arch/arm64/kernel/signal32.c
index 2f507f565c48..e2bdd1eaefd8 100644
--- a/arch/arm64/kernel/signal32.c
+++ b/arch/arm64/kernel/signal32.c
@@ -237,6 +237,10 @@ COMPAT_SYSCALL_DEFINE0(sigreturn)
 	/* Always make any pending restarted system calls return -EINTR */
 	current->restart_block.fn = do_no_restart_syscall;
 
+	/* Reject attempts to call this from a 64-bit process. */
+	if (!is_compat_task())
+		goto badframe;
+
 	/*
 	 * Since we stacked the signal on a 64-bit boundary,
 	 * then 'sp' should be word aligned here.  If it's
@@ -268,6 +272,10 @@ COMPAT_SYSCALL_DEFINE0(rt_sigreturn)
 	/* Always make any pending restarted system calls return -EINTR */
 	current->restart_block.fn = do_no_restart_syscall;
 
+	/* Reject attempts to call this from a 64-bit process. */
+	if (!is_compat_task())
+		goto badframe;
+
 	/*
 	 * Since we stacked the signal on a 64-bit boundary,
 	 * then 'sp' should be word aligned here.  If it's
-- 
2.31.1