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From: Zev Weiss <zev@bewilderbeest.net>
To: Helge Deller <deller@gmx.de>,
	linux-parisc@vger.kernel.org,
	Florent Revest <revest@chromium.org>
Cc: Zev Weiss <zev@bewilderbeest.net>,
	"James E.J. Bottomley" <James.Bottomley@HansenPartnership.com>,
	"Mike Rapoport (IBM)" <rppt@kernel.org>,
	Rick Edgecombe <rick.p.edgecombe@intel.com>,
	"Borislav Petkov (AMD)" <bp@alien8.de>,
	Andrew Morton <akpm@linux-foundation.org>,
	Yang Shi <yang@os.amperecomputing.com>,
	Stefan Roesch <shr@devkernel.io>,
	Oleg Nesterov <oleg@redhat.com>,
	David Hildenbrand <david@redhat.com>,
	Josh Triplett <josh@joshtriplett.org>,
	Ondrej Mosnacek <omosnace@redhat.com>,
	Miguel Ojeda <ojeda@kernel.org>,
	openbmc@lists.ozlabs.org,
	linux-kernel@vger.kernel.org,
	Sam James <sam@gentoo.org>,
	stable@vger.kernel.org
Subject: [PATCH 1/2] prctl: Generalize PR_SET_MDWE support check to be per-arch
Date: Wed,  7 Feb 2024 17:26:19 -0800
Message-ID: <20240208012620.32604-5-zev@bewilderbeest.net>
In-Reply-To: <20240208012620.32604-4-zev@bewilderbeest.net>
References: <20240208012620.32604-4-zev@bewilderbeest.net>
Precedence: bulk
MIME-Version: 1.0
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There exist systems other than PARISC where MDWE may not be feasible
to support; rather than cluttering up the generic code with additional
arch-specific logic let's add a generic function for checking MDWE
support and allow each arch to override it as needed.

Signed-off-by: Zev Weiss <zev@bewilderbeest.net>
Cc: <stable@vger.kernel.org> # v6.3+
---
 arch/parisc/include/asm/mman.h | 14 ++++++++++++++
 include/linux/mman.h           |  8 ++++++++
 kernel/sys.c                   |  7 +++++--
 3 files changed, 27 insertions(+), 2 deletions(-)
 create mode 100644 arch/parisc/include/asm/mman.h

diff --git a/arch/parisc/include/asm/mman.h b/arch/parisc/include/asm/mman.h
new file mode 100644
index 000000000000..47c5a1991d10
--- /dev/null
+++ b/arch/parisc/include/asm/mman.h
@@ -0,0 +1,14 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+#ifndef __ASM_MMAN_H__
+#define __ASM_MMAN_H__
+
+#include <uapi/asm/mman.h>
+
+/* PARISC cannot allow mdwe as it needs writable stacks */
+static inline bool arch_memory_deny_write_exec_supported(void)
+{
+	return false;
+}
+#define arch_memory_deny_write_exec_supported arch_memory_deny_write_exec_supported
+
+#endif /* __ASM_MMAN_H__ */
diff --git a/include/linux/mman.h b/include/linux/mman.h
index dc7048824be8..bcb201ab7a41 100644
--- a/include/linux/mman.h
+++ b/include/linux/mman.h
@@ -162,6 +162,14 @@ calc_vm_flag_bits(unsigned long flags)
 
 unsigned long vm_commit_limit(void);
 
+#ifndef arch_memory_deny_write_exec_supported
+static inline bool arch_memory_deny_write_exec_supported(void)
+{
+	return true;
+}
+#define arch_memory_deny_write_exec_supported arch_memory_deny_write_exec_supported
+#endif
+
 /*
  * Denies creating a writable executable mapping or gaining executable permissions.
  *
diff --git a/kernel/sys.c b/kernel/sys.c
index e219fcfa112d..8d4bd24fa555 100644
--- a/kernel/sys.c
+++ b/kernel/sys.c
@@ -2394,8 +2394,11 @@ static inline int prctl_set_mdwe(unsigned long bits, unsigned long arg3,
 	if (bits & PR_MDWE_NO_INHERIT && !(bits & PR_MDWE_REFUSE_EXEC_GAIN))
 		return -EINVAL;
 
-	/* PARISC cannot allow mdwe as it needs writable stacks */
-	if (IS_ENABLED(CONFIG_PARISC))
+	/*
+	 * EOPNOTSUPP might be more appropriate here in principle, but
+	 * existing userspace depends on EINVAL specifically.
+	 */
+	if (!arch_memory_deny_write_exec_supported())
 		return -EINVAL;
 
 	current_bits = get_current_mdwe();
-- 
2.43.0