Received-SPF: pass (google.com: domain of linux-kernel+bounces-130729-linux.lists.archive=gmail.com@vger.kernel.org designates 139.178.88.99 as permitted sender) client-ip=139.178.88.99;
From: Deepak Gupta <debug@rivosinc.com>
To: paul.walmsley@sifive.com,
	rick.p.edgecombe@intel.com,
	broonie@kernel.org,
	Szabolcs.Nagy@arm.com,
	kito.cheng@sifive.com,
	keescook@chromium.org,
	ajones@ventanamicro.com,
	conor.dooley@microchip.com,
	cleger@rivosinc.com,
	atishp@atishpatra.org,
	alex@ghiti.fr,
	bjorn@rivosinc.com,
	alexghiti@rivosinc.com,
	samuel.holland@sifive.com,
	conor@kernel.org
Cc: linux-doc@vger.kernel.org,
	linux-riscv@lists.infradead.org,
	linux-kernel@vger.kernel.org,
	devicetree@vger.kernel.org,
	linux-mm@kvack.org,
	linux-arch@vger.kernel.org,
	linux-kselftest@vger.kernel.org,
	corbet@lwn.net,
	palmer@dabbelt.com,
	aou@eecs.berkeley.edu,
	robh+dt@kernel.org,
	krzysztof.kozlowski+dt@linaro.org,
	oleg@redhat.com,
	akpm@linux-foundation.org,
	arnd@arndb.de,
	ebiederm@xmission.com,
	Liam.Howlett@oracle.com,
	vbabka@suse.cz,
	lstoakes@gmail.com,
	shuah@kernel.org,
	brauner@kernel.org,
	debug@rivosinc.com,
	andy.chiu@sifive.com,
	jerry.shih@sifive.com,
	hankuan.chen@sifive.com,
	greentime.hu@sifive.com,
	evan@rivosinc.com,
	xiao.w.wang@intel.com,
	charlie@rivosinc.com,
	apatel@ventanamicro.com,
	mchitale@ventanamicro.com,
	dbarboza@ventanamicro.com,
	sameo@rivosinc.com,
	shikemeng@huaweicloud.com,
	willy@infradead.org,
	vincent.chen@sifive.com,
	guoren@kernel.org,
	samitolvanen@google.com,
	songshuaishuai@tinylab.org,
	gerg@kernel.org,
	heiko@sntech.de,
	bhe@redhat.com,
	jeeheng.sia@starfivetech.com,
	cyy@cyyself.name,
	maskray@google.com,
	ancientmodern4@gmail.com,
	mathis.salmen@matsal.de,
	cuiyunhui@bytedance.com,
	bgray@linux.ibm.com,
	mpe@ellerman.id.au,
	baruch@tkos.co.il,
	alx@kernel.org,
	david@redhat.com,
	catalin.marinas@arm.com,
	revest@chromium.org,
	josh@joshtriplett.org,
	shr@devkernel.io,
	deller@gmx.de,
	omosnace@redhat.com,
	ojeda@kernel.org,
	jhubbard@nvidia.com
Subject: [PATCH v3 10/29] riscv/mm : ensure PROT_WRITE leads to VM_READ | VM_WRITE
Date: Wed,  3 Apr 2024 16:34:58 -0700
Message-ID: <20240403234054.2020347-11-debug@rivosinc.com>
In-Reply-To: <20240403234054.2020347-1-debug@rivosinc.com>
References: <20240403234054.2020347-1-debug@rivosinc.com>
Precedence: bulk
MIME-Version: 1.0
Content-Transfer-Encoding: 8bit

`arch_calc_vm_prot_bits` is implemented on risc-v to return VM_READ |
VM_WRITE if PROT_WRITE is specified. Similarly `riscv_sys_mmap` is
updated to convert all incoming PROT_WRITE to (PROT_WRITE | PROT_READ).
This is to make sure that any existing apps using PROT_WRITE still work.

Earlier `protection_map[VM_WRITE]` used to pick read-write PTE encodings.
Now `protection_map[VM_WRITE]` will always pick PAGE_SHADOWSTACK PTE
encodings for shadow stack. Above changes ensure that existing apps
continue to work because underneath kernel will be picking
`protection_map[VM_WRITE|VM_READ]` PTE encodings.

Signed-off-by: Deepak Gupta <debug@rivosinc.com>
---
 arch/riscv/include/asm/mman.h    | 24 ++++++++++++++++++++++++
 arch/riscv/include/asm/pgtable.h |  1 +
 arch/riscv/kernel/sys_riscv.c    | 11 +++++++++++
 arch/riscv/mm/init.c             |  2 +-
 mm/mmap.c                        |  1 +
 5 files changed, 38 insertions(+), 1 deletion(-)
 create mode 100644 arch/riscv/include/asm/mman.h

diff --git a/arch/riscv/include/asm/mman.h b/arch/riscv/include/asm/mman.h
new file mode 100644
index 000000000000..ef9fedf32546
--- /dev/null
+++ b/arch/riscv/include/asm/mman.h
@@ -0,0 +1,24 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+#ifndef __ASM_MMAN_H__
+#define __ASM_MMAN_H__
+
+#include <linux/compiler.h>
+#include <linux/types.h>
+#include <uapi/asm/mman.h>
+
+static inline unsigned long arch_calc_vm_prot_bits(unsigned long prot,
+	unsigned long pkey __always_unused)
+{
+	unsigned long ret = 0;
+
+	/*
+	 * If PROT_WRITE was specified, force it to VM_READ | VM_WRITE.
+	 * Only VM_WRITE means shadow stack.
+	 */
+	if (prot & PROT_WRITE)
+		ret = (VM_READ | VM_WRITE);
+	return ret;
+}
+#define arch_calc_vm_prot_bits(prot, pkey) arch_calc_vm_prot_bits(prot, pkey)
+
+#endif /* ! __ASM_MMAN_H__ */
diff --git a/arch/riscv/include/asm/pgtable.h b/arch/riscv/include/asm/pgtable.h
index 6066822e7396..4d5983bc6766 100644
--- a/arch/riscv/include/asm/pgtable.h
+++ b/arch/riscv/include/asm/pgtable.h
@@ -184,6 +184,7 @@ extern struct pt_alloc_ops pt_ops __initdata;
 #define PAGE_READ_EXEC		__pgprot(_PAGE_BASE | _PAGE_READ | _PAGE_EXEC)
 #define PAGE_WRITE_EXEC		__pgprot(_PAGE_BASE | _PAGE_READ |	\
 					 _PAGE_EXEC | _PAGE_WRITE)
+#define PAGE_SHADOWSTACK       __pgprot(_PAGE_BASE | _PAGE_WRITE)
 
 #define PAGE_COPY		PAGE_READ
 #define PAGE_COPY_EXEC		PAGE_READ_EXEC
diff --git a/arch/riscv/kernel/sys_riscv.c b/arch/riscv/kernel/sys_riscv.c
index f1c1416a9f1e..846c36b1b3d5 100644
--- a/arch/riscv/kernel/sys_riscv.c
+++ b/arch/riscv/kernel/sys_riscv.c
@@ -8,6 +8,8 @@
 #include <linux/syscalls.h>
 #include <asm/cacheflush.h>
 #include <asm-generic/mman-common.h>
+#include <vdso/vsyscall.h>
+#include <asm/mman.h>
 
 static long riscv_sys_mmap(unsigned long addr, unsigned long len,
 			   unsigned long prot, unsigned long flags,
@@ -17,6 +19,15 @@ static long riscv_sys_mmap(unsigned long addr, unsigned long len,
 	if (unlikely(offset & (~PAGE_MASK >> page_shift_offset)))
 		return -EINVAL;
 
+	/*
+	 * If only PROT_WRITE is specified then extend that to PROT_READ
+	 * protection_map[VM_WRITE] is now going to select shadow stack encodings.
+	 * So specifying PROT_WRITE actually should select protection_map [VM_WRITE | VM_READ]
+	 * If user wants to create shadow stack then they should use `map_shadow_stack` syscall.
+	 */
+	if (unlikely((prot & PROT_WRITE) && !(prot & PROT_READ)))
+		prot |= PROT_READ;
+
 	return ksys_mmap_pgoff(addr, len, prot, flags, fd,
 			       offset >> (PAGE_SHIFT - page_shift_offset));
 }
diff --git a/arch/riscv/mm/init.c b/arch/riscv/mm/init.c
index fa34cf55037b..98e5ece4052a 100644
--- a/arch/riscv/mm/init.c
+++ b/arch/riscv/mm/init.c
@@ -299,7 +299,7 @@ pgd_t early_pg_dir[PTRS_PER_PGD] __initdata __aligned(PAGE_SIZE);
 static const pgprot_t protection_map[16] = {
 	[VM_NONE]					= PAGE_NONE,
 	[VM_READ]					= PAGE_READ,
-	[VM_WRITE]					= PAGE_COPY,
+	[VM_WRITE]					= PAGE_SHADOWSTACK,
 	[VM_WRITE | VM_READ]				= PAGE_COPY,
 	[VM_EXEC]					= PAGE_EXEC,
 	[VM_EXEC | VM_READ]				= PAGE_READ_EXEC,
diff --git a/mm/mmap.c b/mm/mmap.c
index d89770eaab6b..57a974f49b00 100644
--- a/mm/mmap.c
+++ b/mm/mmap.c
@@ -47,6 +47,7 @@
 #include <linux/oom.h>
 #include <linux/sched/mm.h>
 #include <linux/ksm.h>
+#include <linux/processor.h>
 
 #include <linux/uaccess.h>
 #include <asm/cacheflush.h>
-- 
2.43.2