From: Mike Rapoport <rppt@kernel.org>
To: Rick Edgecombe <rick.p.edgecombe@intel.com>,
Dave Hansen <dave.hansen@linux.intel.com>
Cc: broonie@kernel.org, akpm@linux-foundation.org,
andrew.cooper3@citrix.com, arnd@arndb.de, bp@alien8.de,
bsingharora@gmail.com, christina.schimpe@intel.com,
corbet@lwn.net, david@redhat.com, debug@rivosinc.com,
dethoma@microsoft.com, eranian@google.com, esyr@redhat.com,
fweimer@redhat.com, gorcunov@gmail.com, hjl.tools@gmail.com,
hpa@zytor.com, jamorris@linux.microsoft.com, jannh@google.com,
john.allen@amd.com, kcc@google.com, keescook@chromium.org,
kirill.shutemov@linux.intel.com, linux-api@vger.kernel.org,
linux-arch@vger.kernel.org, linux-doc@vger.kernel.org,
linux-kernel@vger.kernel.org, linux-mm@kvack.org,
luto@kernel.org, mike.kravetz@oracle.com, mingo@redhat.com,
nadav.amit@gmail.com, oleg@redhat.com, pavel@ucw.cz,
pengfei.xu@intel.com, peterz@infradead.org,
rdunlap@infradead.org, szabolcs.nagy@arm.com, tglx@linutronix.de,
torvalds@linux-foundation.org, weijiang.yang@intel.com,
willy@infradead.org, x86@kernel.org, yu-cheng.yu@intel.com
Subject: Re: [PATCH] x86/shstk: Move arch detail comment out of core mm
Date: Tue, 1 Aug 2023 19:52:21 +0300 [thread overview]
Message-ID: <20230801165221.GA2607694@kernel.org> (raw)
In-Reply-To: <20230706233248.445713-1-rick.p.edgecombe@intel.com>
Hi Dave, Rick,
It seems it didn't get into the current tip.
On Thu, Jul 06, 2023 at 04:32:48PM -0700, Rick Edgecombe wrote:
> The comment around VM_SHADOW_STACK in mm.h refers to a lot of x86
> specific details that don't belong in a cross arch file. Remove these
> out of core mm, and just leave the non-arch details.
>
> Since the comment includes some useful details that would be good to
> retain in the source somewhere, put the arch specifics parts in
> arch/x86/shstk.c near alloc_shstk(), where memory of this type is
> allocated. Include a reference to the existence of the x86 details near
> the VM_SHADOW_STACK definition mm.h.
>
> Signed-off-by: Rick Edgecombe <rick.p.edgecombe@intel.com>
> ---
> arch/x86/kernel/shstk.c | 25 +++++++++++++++++++++++++
> include/linux/mm.h | 32 ++++++--------------------------
> 2 files changed, 31 insertions(+), 26 deletions(-)
>
> diff --git a/arch/x86/kernel/shstk.c b/arch/x86/kernel/shstk.c
> index b26810c7cd1c..47f5204b0fa9 100644
> --- a/arch/x86/kernel/shstk.c
> +++ b/arch/x86/kernel/shstk.c
> @@ -72,6 +72,31 @@ static int create_rstor_token(unsigned long ssp, unsigned long *token_addr)
> return 0;
> }
>
> +/*
> + * VM_SHADOW_STACK will have a guard page. This helps userspace protect
> + * itself from attacks. The reasoning is as follows:
> + *
> + * The shadow stack pointer(SSP) is moved by CALL, RET, and INCSSPQ. The
> + * INCSSP instruction can increment the shadow stack pointer. It is the
> + * shadow stack analog of an instruction like:
> + *
> + * addq $0x80, %rsp
> + *
> + * However, there is one important difference between an ADD on %rsp
> + * and INCSSP. In addition to modifying SSP, INCSSP also reads from the
> + * memory of the first and last elements that were "popped". It can be
> + * thought of as acting like this:
> + *
> + * READ_ONCE(ssp); // read+discard top element on stack
> + * ssp += nr_to_pop * 8; // move the shadow stack
> + * READ_ONCE(ssp-8); // read+discard last popped stack element
> + *
> + * The maximum distance INCSSP can move the SSP is 2040 bytes, before
> + * it would read the memory. Therefore a single page gap will be enough
> + * to prevent any operation from shifting the SSP to an adjacent stack,
> + * since it would have to land in the gap at least once, causing a
> + * fault.
> + */
> static unsigned long alloc_shstk(unsigned long addr, unsigned long size,
> unsigned long token_offset, bool set_res_tok)
> {
> diff --git a/include/linux/mm.h b/include/linux/mm.h
> index 535c58d3b2e4..b647cf2e94ea 100644
> --- a/include/linux/mm.h
> +++ b/include/linux/mm.h
> @@ -343,33 +343,13 @@ extern unsigned int kobjsize(const void *objp);
>
> #ifdef CONFIG_X86_USER_SHADOW_STACK
> /*
> - * This flag should not be set with VM_SHARED because of lack of support
> - * core mm. It will also get a guard page. This helps userspace protect
> - * itself from attacks. The reasoning is as follows:
> + * VM_SHADOW_STACK should not be set with VM_SHARED because of lack of
> + * support core mm.
> *
> - * The shadow stack pointer(SSP) is moved by CALL, RET, and INCSSPQ. The
> - * INCSSP instruction can increment the shadow stack pointer. It is the
> - * shadow stack analog of an instruction like:
> - *
> - * addq $0x80, %rsp
> - *
> - * However, there is one important difference between an ADD on %rsp
> - * and INCSSP. In addition to modifying SSP, INCSSP also reads from the
> - * memory of the first and last elements that were "popped". It can be
> - * thought of as acting like this:
> - *
> - * READ_ONCE(ssp); // read+discard top element on stack
> - * ssp += nr_to_pop * 8; // move the shadow stack
> - * READ_ONCE(ssp-8); // read+discard last popped stack element
> - *
> - * The maximum distance INCSSP can move the SSP is 2040 bytes, before
> - * it would read the memory. Therefore a single page gap will be enough
> - * to prevent any operation from shifting the SSP to an adjacent stack,
> - * since it would have to land in the gap at least once, causing a
> - * fault.
> - *
> - * Prevent using INCSSP to move the SSP between shadow stacks by
> - * having a PAGE_SIZE guard gap.
> + * These VMAs will get a single end guard page. This helps userspace protect
> + * itself from attacks. A single page is enough for current shadow stack archs
> + * (x86). See the comments near alloc_shstk() in arch/x86/kernel/shstk.c
> + * for more details on the guard size.
> */
> # define VM_SHADOW_STACK VM_HIGH_ARCH_5
> #else
> --
> 2.34.1
>
--
Sincerely yours,
Mike.
next prev parent reply other threads:[~2023-08-01 16:53 UTC|newest]
Thread overview: 150+ messages / expand[flat|nested] mbox.gz Atom feed top
2023-06-13 0:10 [PATCH v9 00/42] Shadow stacks for userspace Rick Edgecombe
2023-06-13 0:10 ` [PATCH v9 01/42] mm: Rename arch pte_mkwrite()'s to pte_mkwrite_novma() Rick Edgecombe
2023-06-13 7:19 ` Geert Uytterhoeven
2023-06-13 16:14 ` Edgecombe, Rick P
2023-06-13 7:43 ` Mike Rapoport
2023-06-13 16:14 ` Edgecombe, Rick P
2023-06-13 12:26 ` David Hildenbrand
2023-06-13 16:14 ` Edgecombe, Rick P
2023-07-14 22:57 ` Mark Brown
2023-07-17 15:55 ` Edgecombe, Rick P
2023-07-17 16:51 ` Mark Brown
2023-06-13 0:10 ` [PATCH v9 02/42] mm: Move pte/pmd_mkwrite() callers with no VMA to _novma() Rick Edgecombe
2023-06-13 7:44 ` Mike Rapoport
2023-06-13 16:19 ` Edgecombe, Rick P
2023-06-13 17:00 ` David Hildenbrand
2023-06-14 17:00 ` Edgecombe, Rick P
2023-06-13 12:27 ` David Hildenbrand
2023-06-13 16:20 ` Edgecombe, Rick P
2023-06-13 0:10 ` [PATCH v9 03/42] mm: Make pte_mkwrite() take a VMA Rick Edgecombe
2023-06-13 7:42 ` Mike Rapoport
2023-06-13 16:20 ` Edgecombe, Rick P
2023-06-13 12:28 ` David Hildenbrand
2023-06-13 16:21 ` Edgecombe, Rick P
2023-06-13 0:10 ` [PATCH v9 04/42] mm: Re-introduce vm_flags to do_mmap() Rick Edgecombe
2023-06-14 8:49 ` David Hildenbrand
2023-06-14 23:30 ` Mark Brown
2023-06-13 0:10 ` [PATCH v9 05/42] mm: Move VM_UFFD_MINOR_BIT from 37 to 38 Rick Edgecombe
2023-06-14 8:50 ` David Hildenbrand
2023-06-13 0:10 ` [PATCH v9 06/42] x86/shstk: Add Kconfig option for shadow stack Rick Edgecombe
2023-06-13 0:10 ` [PATCH v9 07/42] x86/traps: Move control protection handler to separate file Rick Edgecombe
2023-06-13 0:10 ` [PATCH v9 08/42] x86/cpufeatures: Add CPU feature flags for shadow stacks Rick Edgecombe
2023-06-13 0:10 ` [PATCH v9 09/42] x86/mm: Move pmd_write(), pud_write() up in the file Rick Edgecombe
2023-06-13 0:10 ` [PATCH v9 10/42] x86/mm: Introduce _PAGE_SAVED_DIRTY Rick Edgecombe
2023-06-13 16:01 ` Edgecombe, Rick P
2023-06-13 17:58 ` Linus Torvalds
2023-06-13 19:37 ` Edgecombe, Rick P
2023-06-13 0:10 ` [PATCH v9 11/42] x86/mm: Update ptep/pmdp_set_wrprotect() for _PAGE_SAVED_DIRTY Rick Edgecombe
2023-06-13 18:01 ` Linus Torvalds
2023-06-13 0:10 ` [PATCH v9 12/42] x86/mm: Start actually marking _PAGE_SAVED_DIRTY Rick Edgecombe
2023-06-13 0:10 ` [PATCH v9 13/42] x86/mm: Remove _PAGE_DIRTY from kernel RO pages Rick Edgecombe
2023-06-13 0:10 ` [PATCH v9 14/42] mm: Introduce VM_SHADOW_STACK for shadow stack memory Rick Edgecombe
2023-06-14 8:50 ` David Hildenbrand
2023-06-14 23:31 ` Mark Brown
2023-06-13 0:10 ` [PATCH v9 15/42] x86/mm: Check shadow stack page fault errors Rick Edgecombe
2023-06-13 0:10 ` [PATCH v9 16/42] mm: Add guard pages around a shadow stack Rick Edgecombe
2023-06-14 23:34 ` Mark Brown
2023-06-22 18:21 ` Matthew Wilcox
2023-06-22 18:27 ` Edgecombe, Rick P
2023-06-23 7:40 ` Mike Rapoport
2023-06-23 12:17 ` Mark Brown
2023-06-25 16:44 ` Edgecombe, Rick P
2023-06-26 12:45 ` Mark Brown
2023-07-06 23:32 ` [PATCH] x86/shstk: Move arch detail comment out of core mm Rick Edgecombe
2023-07-07 15:08 ` Mark Brown
2023-08-01 16:52 ` Mike Rapoport [this message]
2023-06-13 0:10 ` [PATCH v9 17/42] mm: Warn on shadow stack memory in wrong vma Rick Edgecombe
2023-06-14 23:35 ` Mark Brown
2023-06-13 0:10 ` [PATCH v9 18/42] x86/mm: Warn if create Write=0,Dirty=1 with raw prot Rick Edgecombe
2023-06-13 0:10 ` [PATCH v9 19/42] mm/mmap: Add shadow stack pages to memory accounting Rick Edgecombe
2023-06-13 0:10 ` [PATCH v9 20/42] x86/mm: Introduce MAP_ABOVE4G Rick Edgecombe
2023-06-13 0:10 ` [PATCH v9 21/42] x86/mm: Teach pte_mkwrite() about stack memory Rick Edgecombe
2023-06-13 0:10 ` [PATCH v9 22/42] mm: Don't allow write GUPs to shadow " Rick Edgecombe
2023-06-13 0:10 ` [PATCH v9 23/42] Documentation/x86: Add CET shadow stack description Rick Edgecombe
2023-06-13 11:55 ` Mark Brown
2023-06-13 12:37 ` Florian Weimer
2023-06-13 15:15 ` Mark Brown
2023-06-13 17:11 ` Edgecombe, Rick P
2023-06-13 17:57 ` Mark Brown
2023-06-13 19:57 ` Edgecombe, Rick P
2023-06-14 10:43 ` szabolcs.nagy
2023-06-14 16:57 ` Edgecombe, Rick P
2023-06-19 8:47 ` szabolcs.nagy
2023-06-19 16:44 ` Edgecombe, Rick P
2023-06-20 9:17 ` szabolcs.nagy
2023-06-20 19:34 ` Edgecombe, Rick P
2023-06-21 11:36 ` szabolcs.nagy
2023-06-21 18:54 ` Edgecombe, Rick P
2023-06-21 22:22 ` Edgecombe, Rick P
2023-06-21 23:05 ` H.J. Lu
2023-06-21 23:15 ` Edgecombe, Rick P
2023-06-22 1:07 ` Edgecombe, Rick P
2023-06-22 3:23 ` H.J. Lu
2023-06-22 8:27 ` szabolcs.nagy
2023-06-22 16:47 ` Edgecombe, Rick P
2023-06-23 16:25 ` szabolcs.nagy
2023-06-25 18:48 ` Edgecombe, Rick P
2023-06-21 23:02 ` H.J. Lu
2023-06-22 7:40 ` szabolcs.nagy
2023-06-22 16:46 ` Edgecombe, Rick P
2023-06-26 14:08 ` szabolcs.nagy
2023-06-28 1:23 ` Edgecombe, Rick P
2023-06-22 9:18 ` szabolcs.nagy
2023-06-22 15:26 ` Andy Lutomirski
2023-06-22 16:42 ` szabolcs.nagy
2023-06-22 23:18 ` Edgecombe, Rick P
2023-06-29 16:07 ` szabolcs.nagy
2023-07-02 18:03 ` Edgecombe, Rick P
2023-07-03 13:32 ` Mark Brown
2023-07-03 18:19 ` szabolcs.nagy
2023-07-03 18:38 ` Mark Brown
2023-07-03 18:49 ` Florian Weimer
2023-07-04 11:33 ` Szabolcs Nagy
2023-07-05 18:45 ` Edgecombe, Rick P
2023-07-05 19:10 ` Mark Brown
2023-07-05 19:17 ` Edgecombe, Rick P
2023-07-05 19:29 ` Mark Brown
2023-07-06 13:14 ` szabolcs.nagy
2023-07-06 14:24 ` Mark Brown
2023-07-06 16:59 ` Edgecombe, Rick P
2023-07-06 19:03 ` Mark Brown
2023-07-06 13:07 ` szabolcs.nagy
2023-07-06 18:25 ` Edgecombe, Rick P
2023-07-07 15:25 ` szabolcs.nagy
2023-07-07 17:37 ` Edgecombe, Rick P
2023-07-10 16:54 ` szabolcs.nagy
2023-07-10 22:56 ` Edgecombe, Rick P
2023-07-11 8:08 ` szabolcs.nagy
2023-07-12 9:39 ` Szabolcs Nagy
2023-06-25 23:52 ` Andy Lutomirski
2023-06-14 13:12 ` Mark Brown
2023-07-18 19:32 ` Szabolcs Nagy
2023-06-13 0:10 ` [PATCH v9 24/42] x86/fpu/xstate: Introduce CET MSR and XSAVES supervisor states Rick Edgecombe
2023-06-13 0:10 ` [PATCH v9 25/42] x86/fpu: Add helper for modifying xstate Rick Edgecombe
2023-06-13 0:10 ` [PATCH v9 26/42] x86: Introduce userspace API for shadow stack Rick Edgecombe
2023-06-13 0:10 ` [PATCH v9 27/42] x86/shstk: Add user control-protection fault handler Rick Edgecombe
2023-06-13 0:10 ` [PATCH v9 28/42] x86/shstk: Add user-mode shadow stack support Rick Edgecombe
2023-06-27 17:20 ` Mark Brown
2023-06-27 23:46 ` Dave Hansen
2023-06-28 0:37 ` Edgecombe, Rick P
2023-07-06 23:38 ` [PATCH] x86/shstk: Don't retry vm_munmap() on -EINTR Rick Edgecombe
2023-06-13 0:10 ` [PATCH v9 29/42] x86/shstk: Handle thread shadow stack Rick Edgecombe
2023-06-13 0:10 ` [PATCH v9 30/42] x86/shstk: Introduce routines modifying shstk Rick Edgecombe
2023-06-13 0:10 ` [PATCH v9 31/42] x86/shstk: Handle signals for shadow stack Rick Edgecombe
2023-06-13 0:10 ` [PATCH v9 32/42] x86/shstk: Check that SSP is aligned on sigreturn Rick Edgecombe
2023-06-13 0:10 ` [PATCH v9 33/42] x86/shstk: Check that signal frame is shadow stack mem Rick Edgecombe
2023-06-13 0:11 ` [PATCH v9 34/42] x86/shstk: Introduce map_shadow_stack syscall Rick Edgecombe
2023-06-13 0:11 ` [PATCH v9 35/42] x86/shstk: Support WRSS for userspace Rick Edgecombe
2023-06-13 0:11 ` [PATCH v9 36/42] x86: Expose thread features in /proc/$PID/status Rick Edgecombe
2023-06-13 0:11 ` [PATCH v9 37/42] x86/shstk: Wire in shadow stack interface Rick Edgecombe
2023-06-13 0:11 ` [PATCH v9 38/42] x86/cpufeatures: Enable CET CR4 bit for shadow stack Rick Edgecombe
2023-06-13 0:11 ` [PATCH v9 39/42] selftests/x86: Add shadow stack test Rick Edgecombe
2023-06-13 0:11 ` [PATCH v9 40/42] x86: Add PTRACE interface for shadow stack Rick Edgecombe
2023-06-13 0:11 ` [PATCH v9 41/42] x86/shstk: Add ARCH_SHSTK_UNLOCK Rick Edgecombe
2023-06-13 0:11 ` [PATCH v9 42/42] x86/shstk: Add ARCH_SHSTK_STATUS Rick Edgecombe
2023-06-13 1:34 ` [PATCH v9 00/42] Shadow stacks for userspace Linus Torvalds
2023-06-13 3:12 ` Edgecombe, Rick P
2023-06-13 17:44 ` Linus Torvalds
2023-06-13 18:27 ` Linus Torvalds
2023-06-13 19:38 ` Edgecombe, Rick P
2023-06-14 23:45 ` Mark Brown
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