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From: "Kirill A. Shutemov" <kirill@shutemov.name>
To: Yu-cheng Yu <yu-cheng.yu@intel.com>
Cc: x86@kernel.org, "H. Peter Anvin" <hpa@zytor.com>,
	Thomas Gleixner <tglx@linutronix.de>,
	Ingo Molnar <mingo@redhat.com>,
	linux-kernel@vger.kernel.org, linux-doc@vger.kernel.org,
	linux-mm@kvack.org, linux-arch@vger.kernel.org,
	linux-api@vger.kernel.org, Arnd Bergmann <arnd@arndb.de>,
	Andy Lutomirski <luto@kernel.org>,
	Balbir Singh <bsingharora@gmail.com>,
	Borislav Petkov <bp@alien8.de>,
	Cyrill Gorcunov <gorcunov@gmail.com>,
	Dave Hansen <dave.hansen@linux.intel.com>,
	Eugene Syromiatnikov <esyr@redhat.com>,
	Florian Weimer <fweimer@redhat.com>,
	"H.J. Lu" <hjl.tools@gmail.com>, Jann Horn <jannh@google.com>,
	Jonathan Corbet <corbet@lwn.net>,
	Kees Cook <keescook@chromium.org>,
	Mike Kravetz <mike.kravetz@oracle.com>,
	Nadav Amit <nadav.amit@gmail.com>,
	Oleg Nesterov <oleg@redhat.com>, Pavel Machek <pavel@ucw.cz>,
	Peter Zijlstra <peterz@infradead.org>,
	Randy Dunlap <rdunlap@infradead.org>,
	"Ravi V. Shankar" <ravi.v.shankar@intel.com>,
	Vedvyas Shanbhogue <vedvyas.shanbhogue@intel.com>,
	Dave Martin <Dave.Martin@arm.com>,
	Weijiang Yang <weijiang.yang@intel.com>,
	Pengfei Xu <pengfei.xu@intel.com>,
	Haitao Huang <haitao.huang@intel.com>,
	"Kirill A . Shutemov" <kirill.shutemov@linux.intel.com>
Subject: Re: [PATCH v25 30/30] mm: Introduce PROT_SHSTK for shadow stack
Date: Mon, 26 Apr 2021 09:52:43 +0300	[thread overview]
Message-ID: <20210426065243.ozh6doz6q5xonrqe@box.shutemov.name> (raw)
In-Reply-To: <20210415221419.31835-31-yu-cheng.yu@intel.com>

On Thu, Apr 15, 2021 at 03:14:19PM -0700, Yu-cheng Yu wrote:
> There are three possible options to create a shadow stack allocation API:
> an arch_prctl, a new syscall, or adding PROT_SHSTK to mmap()/mprotect().
> Each has its advantages and compromises.
> 
> An arch_prctl() is the least intrusive.  However, the existing x86
> arch_prctl() takes only two parameters.  Multiple parameters must be
> passed in a memory buffer.  There is a proposal to pass more parameters in
> registers [1], but no active discussion on that.
> 
> A new syscall minimizes compatibility issues and offers an extensible frame
> work to other architectures, but this will likely result in some overlap of
> mmap()/mprotect().
> 
> The introduction of PROT_SHSTK to mmap()/mprotect() takes advantage of

Maybe PROT_SHADOW_STACK?

> existing APIs.  The x86-specific PROT_SHSTK is translated to
> VM_SHADOW_STACK and a shadow stack mapping is created without reinventing
> the wheel.  There are potential pitfalls though.  The most obvious one
> would be using this as a bypass to shadow stack protection.  However, the
> attacker would have to get to the syscall first.
> 
> [1] https://lore.kernel.org/lkml/20200828121624.108243-1-hjl.tools@gmail.com/
> 
> Signed-off-by: Yu-cheng Yu <yu-cheng.yu@intel.com>
> Cc: Kees Cook <keescook@chromium.org>
> Cc: Kirill A. Shutemov <kirill.shutemov@linux.intel.com>
> ---
> v24:
> - Update arch_calc_vm_prot_bits(), leave PROT* checking to
>   arch_validate_prot().
> - Update arch_validate_prot(), leave vma flags checking to
>   arch_validate_flags().
> - Add arch_validate_flags().
> 
>  arch/x86/include/asm/mman.h      | 59 +++++++++++++++++++++++++++++++-
>  arch/x86/include/uapi/asm/mman.h |  1 +
>  include/linux/mm.h               |  1 +
>  3 files changed, 60 insertions(+), 1 deletion(-)
> 
> diff --git a/arch/x86/include/asm/mman.h b/arch/x86/include/asm/mman.h
> index 629f6c81263a..1821c179f35d 100644
> --- a/arch/x86/include/asm/mman.h
> +++ b/arch/x86/include/asm/mman.h
> @@ -20,11 +20,68 @@
>  		((vm_flags) & VM_PKEY_BIT2 ? _PAGE_PKEY_BIT2 : 0) |	\
>  		((vm_flags) & VM_PKEY_BIT3 ? _PAGE_PKEY_BIT3 : 0))
>  
> -#define arch_calc_vm_prot_bits(prot, key) (		\
> +#define pkey_vm_prot_bits(prot, key) (			\
>  		((key) & 0x1 ? VM_PKEY_BIT0 : 0) |      \
>  		((key) & 0x2 ? VM_PKEY_BIT1 : 0) |      \
>  		((key) & 0x4 ? VM_PKEY_BIT2 : 0) |      \
>  		((key) & 0x8 ? VM_PKEY_BIT3 : 0))
> +#else
> +#define pkey_vm_prot_bits(prot, key) (0)
>  #endif
>  
> +static inline unsigned long arch_calc_vm_prot_bits(unsigned long prot,
> +						   unsigned long pkey)
> +{
> +	unsigned long vm_prot_bits = pkey_vm_prot_bits(prot, pkey);
> +
> +	if (prot & PROT_SHSTK)
> +		vm_prot_bits |= VM_SHADOW_STACK;
> +
> +	return vm_prot_bits;
> +}
> +
> +#define arch_calc_vm_prot_bits(prot, pkey) arch_calc_vm_prot_bits(prot, pkey)
> +
> +#ifdef CONFIG_X86_SHADOW_STACK
> +static inline bool arch_validate_prot(unsigned long prot, unsigned long addr)
> +{
> +	unsigned long valid = PROT_READ | PROT_WRITE | PROT_EXEC | PROT_SEM |
> +			      PROT_SHSTK;
> +
> +	if (prot & ~valid)
> +		return false;
> +
> +	if (prot & PROT_SHSTK) {
> +		if (!current->thread.cet.shstk_size)
> +			return false;
> +
> +		/*
> +		 * A shadow stack mapping is indirectly writable by only
> +		 * the CALL and WRUSS instructions, but not other write
> +		 * instructions).  PROT_SHSTK and PROT_WRITE are mutually
> +		 * exclusive.
> +		 */
> +		if (prot & PROT_WRITE)
> +			return false;
> +	}
> +
> +	return true;
> +}
> +
> +#define arch_validate_prot arch_validate_prot
> +
> +static inline bool arch_validate_flags(unsigned long vm_flags, bool is_anon)
> +{
> +	if (vm_flags & VM_SHADOW_STACK) {
> +		if ((vm_flags & VM_SHARED) || !is_anon)

VM_SHARED check is redundant. vma_is_anonymous() should be enough.
Anonymous shared mappings would fail vma_is_anonymous().

> +			return false;
> +	}
> +
> +	return true;
> +}
> +
> +#define arch_validate_flags(vm_flags, is_anon) arch_validate_flags(vm_flags, is_anon)
> +
> +#endif /* CONFIG_X86_SHADOW_STACK */
> +
>  #endif /* _ASM_X86_MMAN_H */
> diff --git a/arch/x86/include/uapi/asm/mman.h b/arch/x86/include/uapi/asm/mman.h
> index 3ce1923e6ed9..39bb7db344a6 100644
> --- a/arch/x86/include/uapi/asm/mman.h
> +++ b/arch/x86/include/uapi/asm/mman.h
> @@ -4,6 +4,7 @@
>  
>  #define MAP_32BIT	0x40		/* only give out 32bit addresses */
>  
> +#define PROT_SHSTK	0x10		/* shadow stack pages */
>  
>  #include <asm-generic/mman.h>
>  
> diff --git a/include/linux/mm.h b/include/linux/mm.h
> index 1ccec5cc399b..9a7652eea207 100644
> --- a/include/linux/mm.h
> +++ b/include/linux/mm.h
> @@ -342,6 +342,7 @@ extern unsigned int kobjsize(const void *objp);
>  
>  #if defined(CONFIG_X86)
>  # define VM_PAT		VM_ARCH_1	/* PAT reserves whole VMA at once (x86) */
> +# define VM_ARCH_CLEAR	VM_SHADOW_STACK
>  #elif defined(CONFIG_PPC)
>  # define VM_SAO		VM_ARCH_1	/* Strong Access Ordering (powerpc) */
>  #elif defined(CONFIG_PARISC)
> -- 
> 2.21.0
> 
> 

-- 
 Kirill A. Shutemov

  reply	other threads:[~2021-04-26  6:52 UTC|newest]

Thread overview: 43+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2021-04-15 22:13 [PATCH v25 00/30] Control-flow Enforcement: Shadow Stack Yu-cheng Yu
2021-04-15 22:13 ` [PATCH v25 01/30] Documentation/x86: Add CET description Yu-cheng Yu
2021-04-15 22:13 ` [PATCH v25 02/30] x86/cet/shstk: Add Kconfig option for Shadow Stack Yu-cheng Yu
2021-04-15 22:13 ` [PATCH v25 03/30] x86/cpufeatures: Add CET CPU feature flags for Control-flow Enforcement Technology (CET) Yu-cheng Yu
2021-04-15 22:13 ` [PATCH v25 04/30] x86/cpufeatures: Introduce CPU setup and option parsing for CET Yu-cheng Yu
2021-04-15 22:13 ` [PATCH v25 05/30] x86/fpu/xstate: Introduce CET MSR and XSAVES supervisor states Yu-cheng Yu
2021-04-15 22:13 ` [PATCH v25 06/30] x86/cet: Add control-protection fault handler Yu-cheng Yu
2021-04-15 22:13 ` [PATCH v25 07/30] x86/mm: Remove _PAGE_DIRTY from kernel RO pages Yu-cheng Yu
2021-04-15 22:13 ` [PATCH v25 08/30] x86/mm: Move pmd_write(), pud_write() up in the file Yu-cheng Yu
2021-04-15 22:13 ` [PATCH v25 09/30] x86/mm: Introduce _PAGE_COW Yu-cheng Yu
2021-04-15 22:13 ` [PATCH v25 10/30] drm/i915/gvt: Change _PAGE_DIRTY to _PAGE_DIRTY_BITS Yu-cheng Yu
2021-04-15 22:14 ` [PATCH v25 11/30] x86/mm: Update pte_modify for _PAGE_COW Yu-cheng Yu
2021-04-15 22:14 ` [PATCH v25 12/30] x86/mm: Update ptep_set_wrprotect() and pmdp_set_wrprotect() for transition from _PAGE_DIRTY to _PAGE_COW Yu-cheng Yu
2021-04-15 22:14 ` [PATCH v25 13/30] mm: Introduce VM_SHADOW_STACK for shadow stack memory Yu-cheng Yu
2021-04-15 22:14 ` [PATCH v25 14/30] x86/mm: Shadow Stack page fault error checking Yu-cheng Yu
2021-04-15 22:14 ` [PATCH v25 15/30] x86/mm: Update maybe_mkwrite() for shadow stack Yu-cheng Yu
2021-04-15 22:14 ` [PATCH v25 16/30] mm: Fixup places that call pte_mkwrite() directly Yu-cheng Yu
2021-04-23 10:13   ` Kirill A. Shutemov
2021-04-15 22:14 ` [PATCH v25 17/30] mm: Add guard pages around a shadow stack Yu-cheng Yu
2021-04-15 22:14 ` [PATCH v25 18/30] mm/mmap: Add shadow stack pages to memory accounting Yu-cheng Yu
2021-04-23 10:19   ` Kirill A. Shutemov
2021-04-15 22:14 ` [PATCH v25 19/30] mm: Update can_follow_write_pte() for shadow stack Yu-cheng Yu
2021-04-23 10:25   ` Kirill A. Shutemov
2021-04-15 22:14 ` [PATCH v25 20/30] mm/mprotect: Exclude shadow stack from preserve_write Yu-cheng Yu
2021-04-23 10:27   ` Kirill A. Shutemov
2021-04-15 22:14 ` [PATCH v25 21/30] mm: Re-introduce vm_flags to do_mmap() Yu-cheng Yu
2021-04-23 10:31   ` Kirill A. Shutemov
2021-04-23 15:59     ` Yu, Yu-cheng
2021-04-15 22:14 ` [PATCH v25 22/30] x86/cet/shstk: Add user-mode shadow stack support Yu-cheng Yu
2021-04-15 22:14 ` [PATCH v25 23/30] x86/cet/shstk: Handle thread shadow stack Yu-cheng Yu
2021-04-15 22:14 ` [PATCH v25 24/30] x86/cet/shstk: Introduce shadow stack token setup/verify routines Yu-cheng Yu
2021-04-15 22:14 ` [PATCH v25 25/30] x86/cet/shstk: Handle signals for shadow stack Yu-cheng Yu
2021-04-15 22:14 ` [PATCH v25 26/30] ELF: Introduce arch_setup_elf_property() Yu-cheng Yu
2021-04-15 22:14 ` [PATCH v25 27/30] x86/cet/shstk: Add arch_prctl functions for shadow stack Yu-cheng Yu
2021-04-15 22:14 ` [PATCH v25 28/30] mm: Move arch_calc_vm_prot_bits() to arch/x86/include/asm/mman.h Yu-cheng Yu
2021-04-26  6:31   ` Kirill A. Shutemov
2021-04-15 22:14 ` [PATCH v25 29/30] mm: Update arch_validate_flags() to include vma anonymous Yu-cheng Yu
2021-04-26  6:40   ` Kirill A. Shutemov
2021-04-26 11:11     ` Catalin Marinas
2021-04-26 17:56       ` Yu, Yu-cheng
2021-04-15 22:14 ` [PATCH v25 30/30] mm: Introduce PROT_SHSTK for shadow stack Yu-cheng Yu
2021-04-26  6:52   ` Kirill A. Shutemov [this message]
2021-04-26 18:00     ` Yu, Yu-cheng

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