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Message-ID: <CANXhq0pE+o4C_mn-Ofkf8uqEUJ+9SCpv5+z8zaSVQi0nW3558Q@mail.gmail.com>
Date: Fri, 14 Mar 2025 16:28:39 +0800
From: Zong Li <zong.li@...ive.com>
To: Deepak Gupta <debug@...osinc.com>
Cc: Thomas Gleixner <tglx@...utronix.de>, Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
Dave Hansen <dave.hansen@...ux.intel.com>, x86@...nel.org,
"H. Peter Anvin" <hpa@...or.com>, Andrew Morton <akpm@...ux-foundation.org>,
"Liam R. Howlett" <Liam.Howlett@...cle.com>, Vlastimil Babka <vbabka@...e.cz>,
Lorenzo Stoakes <lorenzo.stoakes@...cle.com>, Paul Walmsley <paul.walmsley@...ive.com>,
Palmer Dabbelt <palmer@...belt.com>, Albert Ou <aou@...s.berkeley.edu>,
Conor Dooley <conor@...nel.org>, Rob Herring <robh@...nel.org>,
Krzysztof Kozlowski <krzk+dt@...nel.org>, Arnd Bergmann <arnd@...db.de>,
Christian Brauner <brauner@...nel.org>, Peter Zijlstra <peterz@...radead.org>,
Oleg Nesterov <oleg@...hat.com>, Eric Biederman <ebiederm@...ssion.com>, Kees Cook <kees@...nel.org>,
Jonathan Corbet <corbet@....net>, Shuah Khan <shuah@...nel.org>, Jann Horn <jannh@...gle.com>,
Conor Dooley <conor+dt@...nel.org>, linux-kernel@...r.kernel.org,
linux-fsdevel@...r.kernel.org, linux-mm@...ck.org,
linux-riscv@...ts.infradead.org, devicetree@...r.kernel.org,
linux-arch@...r.kernel.org, linux-doc@...r.kernel.org,
linux-kselftest@...r.kernel.org, alistair.francis@....com,
richard.henderson@...aro.org, jim.shu@...ive.com, andybnac@...il.com,
kito.cheng@...ive.com, charlie@...osinc.com, atishp@...osinc.com,
evan@...osinc.com, cleger@...osinc.com, alexghiti@...osinc.com,
samitolvanen@...gle.com, broonie@...nel.org, rick.p.edgecombe@...el.com
Subject: Re: [PATCH v11 06/27] riscv/mm : ensure PROT_WRITE leads to VM_READ | VM_WRITE
On Mon, Mar 10, 2025 at 11:42 PM Deepak Gupta <debug@...osinc.com> wrote:
>
> `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@...osinc.com>
> ---
> arch/riscv/include/asm/mman.h | 25 +++++++++++++++++++++++++
> arch/riscv/include/asm/pgtable.h | 1 +
> arch/riscv/kernel/sys_riscv.c | 10 ++++++++++
> arch/riscv/mm/init.c | 2 +-
> 4 files changed, 37 insertions(+), 1 deletion(-)
>
> diff --git a/arch/riscv/include/asm/mman.h b/arch/riscv/include/asm/mman.h
> new file mode 100644
> index 000000000000..392c9c2d2e78
> --- /dev/null
> +++ b/arch/riscv/include/asm/mman.h
> @@ -0,0 +1,25 @@
> +/* 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 050fdc49b5ad..8c528cd7347a 100644
> --- a/arch/riscv/include/asm/pgtable.h
> +++ b/arch/riscv/include/asm/pgtable.h
> @@ -178,6 +178,7 @@ extern struct pt_alloc_ops pt_ops __meminitdata;
> #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 d77afe05578f..43a448bf254b 100644
> --- a/arch/riscv/kernel/sys_riscv.c
> +++ b/arch/riscv/kernel/sys_riscv.c
> @@ -7,6 +7,7 @@
>
> #include <linux/syscalls.h>
> #include <asm/cacheflush.h>
> +#include <asm-generic/mman-common.h>
>
> static long riscv_sys_mmap(unsigned long addr, unsigned long len,
> unsigned long prot, unsigned long flags,
> @@ -16,6 +17,15 @@ static long riscv_sys_mmap(unsigned long addr, unsigned long len,
> if (unlikely(offset & (~PAGE_MASK >> page_shift_offset)))
> return -EINVAL;
>
> + /*
> + * If 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 15b2eda4c364..9d6661638d0b 100644
> --- a/arch/riscv/mm/init.c
> +++ b/arch/riscv/mm/init.c
> @@ -342,7 +342,7 @@ 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,
>
LGTM.
Reviewed-by: Zong Li <zong.li@...ive.com>
> --
> 2.34.1
>
>
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