From: Dan Williams <dan.j.williams@intel.com> To: linux-kernel@vger.kernel.org Cc: linux-arch@vger.kernel.org, Kees Cook <keescook@chromium.org>, kernel-hardening@lists.openwall.com, gregkh@linuxfoundation.org, x86@kernel.org, Ingo Molnar <mingo@redhat.com>, Al Viro <viro@zeniv.linux.org.uk>, "H. Peter Anvin" <hpa@zytor.com>, tglx@linutronix.de, torvalds@linux-foundation.org, akpm@linux-foundation.org, alan@linux.intel.com Subject: [PATCH v4 06/10] x86, get_user: use pointer masking to limit speculation Date: Thu, 18 Jan 2018 16:02:15 -0800 [thread overview] Message-ID: <151632013524.21271.4516878993060956547.stgit@dwillia2-desk3.amr.corp.intel.com> (raw) In-Reply-To: <151632009605.21271.11304291057104672116.stgit@dwillia2-desk3.amr.corp.intel.com> Quoting Linus: I do think that it would be a good idea to very expressly document the fact that it's not that the user access itself is unsafe. I do agree that things like "get_user()" want to be protected, but not because of any direct bugs or problems with get_user() and friends, but simply because get_user() is an excellent source of a pointer that is obviously controlled from a potentially attacking user space. So it's a prime candidate for then finding _subsequent_ accesses that can then be used to perturb the cache. Unlike the '__get_user' case 'get_user' includes the address limit check near the pointer de-reference. With that locality the speculation can be mitigated with pointer narrowing rather than a barrier. Where the narrowing is performed by: cmp %limit, %ptr sbb %mask, %mask and %mask, %ptr With respect to speculation the value of %ptr is either less than %limit or NULL. Co-developed-by: Linus Torvalds <torvalds@linux-foundation.org> Cc: Al Viro <viro@zeniv.linux.org.uk> Cc: Kees Cook <keescook@chromium.org> Cc: Thomas Gleixner <tglx@linutronix.de> Cc: "H. Peter Anvin" <hpa@zytor.com> Cc: Ingo Molnar <mingo@redhat.com> Cc: x86@kernel.org Signed-off-by: Dan Williams <dan.j.williams@intel.com> --- arch/x86/include/asm/smap.h | 17 +++++++++++++++++ arch/x86/lib/getuser.S | 5 +++++ 2 files changed, 22 insertions(+) diff --git a/arch/x86/include/asm/smap.h b/arch/x86/include/asm/smap.h index db333300bd4b..2b4ad4c6a226 100644 --- a/arch/x86/include/asm/smap.h +++ b/arch/x86/include/asm/smap.h @@ -25,6 +25,23 @@ #include <asm/alternative-asm.h> +/* + * MASK_NOSPEC - sanitize the value of a user controlled value with + * respect to speculation + * + * In the get_user path once we have determined that the pointer is + * below the current address limit sanitize its value with respect to + * speculation. In the case when the pointer is above the address limit + * this directs the cpu to speculate with a NULL ptr rather than + * something targeting kernel memory. + * + * assumes CF is set from a previous 'cmp TASK_addr_limit, %ptr' + */ +.macro MASK_NOSPEC mask val + sbb \mask, \mask + and \mask, \val +.endm + #ifdef CONFIG_X86_SMAP #define ASM_CLAC \ diff --git a/arch/x86/lib/getuser.S b/arch/x86/lib/getuser.S index c97d935a29e8..07d0e8a28b17 100644 --- a/arch/x86/lib/getuser.S +++ b/arch/x86/lib/getuser.S @@ -40,6 +40,7 @@ ENTRY(__get_user_1) mov PER_CPU_VAR(current_task), %_ASM_DX cmp TASK_addr_limit(%_ASM_DX),%_ASM_AX jae bad_get_user + MASK_NOSPEC %_ASM_DX, %_ASM_AX ASM_STAC 1: movzbl (%_ASM_AX),%edx xor %eax,%eax @@ -54,6 +55,7 @@ ENTRY(__get_user_2) mov PER_CPU_VAR(current_task), %_ASM_DX cmp TASK_addr_limit(%_ASM_DX),%_ASM_AX jae bad_get_user + MASK_NOSPEC %_ASM_DX, %_ASM_AX ASM_STAC 2: movzwl -1(%_ASM_AX),%edx xor %eax,%eax @@ -68,6 +70,7 @@ ENTRY(__get_user_4) mov PER_CPU_VAR(current_task), %_ASM_DX cmp TASK_addr_limit(%_ASM_DX),%_ASM_AX jae bad_get_user + MASK_NOSPEC %_ASM_DX, %_ASM_AX ASM_STAC 3: movl -3(%_ASM_AX),%edx xor %eax,%eax @@ -83,6 +86,7 @@ ENTRY(__get_user_8) mov PER_CPU_VAR(current_task), %_ASM_DX cmp TASK_addr_limit(%_ASM_DX),%_ASM_AX jae bad_get_user + MASK_NOSPEC %_ASM_DX, %_ASM_AX ASM_STAC 4: movq -7(%_ASM_AX),%rdx xor %eax,%eax @@ -94,6 +98,7 @@ ENTRY(__get_user_8) mov PER_CPU_VAR(current_task), %_ASM_DX cmp TASK_addr_limit(%_ASM_DX),%_ASM_AX jae bad_get_user_8 + MASK_NOSPEC %_ASM_DX, %_ASM_AX ASM_STAC 4: movl -7(%_ASM_AX),%edx 5: movl -3(%_ASM_AX),%ecx
WARNING: multiple messages have this Message-ID (diff)
From: Dan Williams <dan.j.williams@intel.com> To: linux-kernel@vger.kernel.org Cc: linux-arch@vger.kernel.org, Kees Cook <keescook@chromium.org>, kernel-hardening@lists.openwall.com, gregkh@linuxfoundation.org, x86@kernel.org, Ingo Molnar <mingo@redhat.com>, Al Viro <viro@zeniv.linux.org.uk>, "H. Peter Anvin" <hpa@zytor.com>, tglx@linutronix.de, torvalds@linux-foundation.org, akpm@linux-foundation.org, alan@linux.intel.com Subject: [kernel-hardening] [PATCH v4 06/10] x86, get_user: use pointer masking to limit speculation Date: Thu, 18 Jan 2018 16:02:15 -0800 [thread overview] Message-ID: <151632013524.21271.4516878993060956547.stgit@dwillia2-desk3.amr.corp.intel.com> (raw) In-Reply-To: <151632009605.21271.11304291057104672116.stgit@dwillia2-desk3.amr.corp.intel.com> Quoting Linus: I do think that it would be a good idea to very expressly document the fact that it's not that the user access itself is unsafe. I do agree that things like "get_user()" want to be protected, but not because of any direct bugs or problems with get_user() and friends, but simply because get_user() is an excellent source of a pointer that is obviously controlled from a potentially attacking user space. So it's a prime candidate for then finding _subsequent_ accesses that can then be used to perturb the cache. Unlike the '__get_user' case 'get_user' includes the address limit check near the pointer de-reference. With that locality the speculation can be mitigated with pointer narrowing rather than a barrier. Where the narrowing is performed by: cmp %limit, %ptr sbb %mask, %mask and %mask, %ptr With respect to speculation the value of %ptr is either less than %limit or NULL. Co-developed-by: Linus Torvalds <torvalds@linux-foundation.org> Cc: Al Viro <viro@zeniv.linux.org.uk> Cc: Kees Cook <keescook@chromium.org> Cc: Thomas Gleixner <tglx@linutronix.de> Cc: "H. Peter Anvin" <hpa@zytor.com> Cc: Ingo Molnar <mingo@redhat.com> Cc: x86@kernel.org Signed-off-by: Dan Williams <dan.j.williams@intel.com> --- arch/x86/include/asm/smap.h | 17 +++++++++++++++++ arch/x86/lib/getuser.S | 5 +++++ 2 files changed, 22 insertions(+) diff --git a/arch/x86/include/asm/smap.h b/arch/x86/include/asm/smap.h index db333300bd4b..2b4ad4c6a226 100644 --- a/arch/x86/include/asm/smap.h +++ b/arch/x86/include/asm/smap.h @@ -25,6 +25,23 @@ #include <asm/alternative-asm.h> +/* + * MASK_NOSPEC - sanitize the value of a user controlled value with + * respect to speculation + * + * In the get_user path once we have determined that the pointer is + * below the current address limit sanitize its value with respect to + * speculation. In the case when the pointer is above the address limit + * this directs the cpu to speculate with a NULL ptr rather than + * something targeting kernel memory. + * + * assumes CF is set from a previous 'cmp TASK_addr_limit, %ptr' + */ +.macro MASK_NOSPEC mask val + sbb \mask, \mask + and \mask, \val +.endm + #ifdef CONFIG_X86_SMAP #define ASM_CLAC \ diff --git a/arch/x86/lib/getuser.S b/arch/x86/lib/getuser.S index c97d935a29e8..07d0e8a28b17 100644 --- a/arch/x86/lib/getuser.S +++ b/arch/x86/lib/getuser.S @@ -40,6 +40,7 @@ ENTRY(__get_user_1) mov PER_CPU_VAR(current_task), %_ASM_DX cmp TASK_addr_limit(%_ASM_DX),%_ASM_AX jae bad_get_user + MASK_NOSPEC %_ASM_DX, %_ASM_AX ASM_STAC 1: movzbl (%_ASM_AX),%edx xor %eax,%eax @@ -54,6 +55,7 @@ ENTRY(__get_user_2) mov PER_CPU_VAR(current_task), %_ASM_DX cmp TASK_addr_limit(%_ASM_DX),%_ASM_AX jae bad_get_user + MASK_NOSPEC %_ASM_DX, %_ASM_AX ASM_STAC 2: movzwl -1(%_ASM_AX),%edx xor %eax,%eax @@ -68,6 +70,7 @@ ENTRY(__get_user_4) mov PER_CPU_VAR(current_task), %_ASM_DX cmp TASK_addr_limit(%_ASM_DX),%_ASM_AX jae bad_get_user + MASK_NOSPEC %_ASM_DX, %_ASM_AX ASM_STAC 3: movl -3(%_ASM_AX),%edx xor %eax,%eax @@ -83,6 +86,7 @@ ENTRY(__get_user_8) mov PER_CPU_VAR(current_task), %_ASM_DX cmp TASK_addr_limit(%_ASM_DX),%_ASM_AX jae bad_get_user + MASK_NOSPEC %_ASM_DX, %_ASM_AX ASM_STAC 4: movq -7(%_ASM_AX),%rdx xor %eax,%eax @@ -94,6 +98,7 @@ ENTRY(__get_user_8) mov PER_CPU_VAR(current_task), %_ASM_DX cmp TASK_addr_limit(%_ASM_DX),%_ASM_AX jae bad_get_user_8 + MASK_NOSPEC %_ASM_DX, %_ASM_AX ASM_STAC 4: movl -7(%_ASM_AX),%edx 5: movl -3(%_ASM_AX),%ecx
next prev parent reply other threads:[~2018-01-19 0:02 UTC|newest] Thread overview: 70+ messages / expand[flat|nested] mbox.gz Atom feed top 2018-01-19 0:01 [PATCH v4 00/10] prevent bounds-check bypass via speculative execution Dan Williams 2018-01-19 0:01 ` [kernel-hardening] " Dan Williams 2018-01-19 0:01 ` Dan Williams 2018-01-19 0:01 ` [PATCH v4 01/10] Documentation: document array_ptr Dan Williams 2018-01-19 0:01 ` [kernel-hardening] " Dan Williams 2018-01-19 0:01 ` [PATCH v4 02/10] asm/nospec, array_ptr: sanitize speculative array de-references Dan Williams 2018-01-19 0:01 ` [kernel-hardening] " Dan Williams 2018-01-19 10:20 ` Jann Horn 2018-01-19 17:48 ` Adam Sampson 2018-01-19 17:48 ` Adam Sampson 2018-01-19 17:48 ` Adam Sampson 2018-01-19 17:48 ` Adam Sampson 2018-01-19 18:12 ` Dan Williams 2018-01-19 18:18 ` Will Deacon 2018-01-19 18:18 ` Will Deacon 2018-01-19 18:26 ` [kernel-hardening] " Dan Williams 2018-01-19 18:18 ` Linus Torvalds 2018-01-19 18:18 ` Linus Torvalds 2018-01-19 20:55 ` [kernel-hardening] " Dan Williams 2018-01-25 7:09 ` Cyril Novikov 2018-01-25 7:09 ` [kernel-hardening] " Cyril Novikov 2018-01-25 22:37 ` Dan Williams 2018-01-25 22:37 ` [kernel-hardening] " Dan Williams 2018-01-19 0:01 ` [PATCH v4 03/10] x86: implement array_ptr_mask() Dan Williams 2018-01-19 0:01 ` [kernel-hardening] " Dan Williams 2018-01-19 0:01 ` [PATCH v4 04/10] x86: introduce __uaccess_begin_nospec and ifence Dan Williams 2018-01-19 0:01 ` [kernel-hardening] " Dan Williams 2018-01-19 0:02 ` [PATCH v4 05/10] x86, __get_user: use __uaccess_begin_nospec Dan Williams 2018-01-19 0:02 ` [kernel-hardening] " Dan Williams 2018-01-19 0:02 ` Dan Williams [this message] 2018-01-19 0:02 ` [kernel-hardening] [PATCH v4 06/10] x86, get_user: use pointer masking to limit speculation Dan Williams 2018-01-19 0:02 ` [PATCH v4 07/10] x86: narrow out of bounds syscalls to sys_read under speculation Dan Williams 2018-01-19 0:02 ` [kernel-hardening] " Dan Williams 2018-01-24 14:40 ` Jiri Slaby 2018-01-24 14:40 ` [kernel-hardening] " Jiri Slaby 2018-02-06 19:29 ` Luis Henriques 2018-02-06 19:48 ` Dan Williams 2018-02-06 20:26 ` Linus Torvalds 2018-02-06 20:37 ` Dan Williams 2018-02-06 20:42 ` Linus Torvalds 2018-02-06 20:43 ` Linus Torvalds 2018-02-06 20:49 ` Andy Lutomirski 2018-02-06 20:58 ` Linus Torvalds 2018-02-06 21:37 ` Dan Williams 2018-02-06 22:52 ` Linus Torvalds 2018-02-07 0:33 ` Dan Williams 2018-02-07 1:23 ` Linus Torvalds 2018-02-06 22:51 ` Luis Henriques 2018-02-06 22:51 ` Luis Henriques 2018-01-19 0:02 ` [PATCH v4 08/10] vfs, fdtable: prevent bounds-check bypass via speculative execution Dan Williams 2018-01-19 0:02 ` [kernel-hardening] " Dan Williams 2018-01-19 0:02 ` [PATCH v4 09/10] kvm, x86: fix spectre-v1 mitigation Dan Williams 2018-01-19 0:02 ` [kernel-hardening] " Dan Williams 2018-01-19 8:42 ` Paolo Bonzini 2018-01-19 8:42 ` [kernel-hardening] " Paolo Bonzini 2018-01-19 0:02 ` [PATCH v4 10/10] nl80211: sanitize array index in parse_txq_params Dan Williams 2018-01-19 0:02 ` [kernel-hardening] " Dan Williams 2018-01-19 0:02 ` Dan Williams 2018-01-21 10:37 ` Johannes Berg 2018-01-21 10:37 ` [kernel-hardening] " Johannes Berg 2018-01-21 10:37 ` Johannes Berg 2018-01-20 6:58 ` [PATCH v4 00/10] prevent bounds-check bypass via speculative execution Dan Williams 2018-01-20 6:58 ` [kernel-hardening] " Dan Williams 2018-01-20 6:58 ` Dan Williams 2018-01-20 16:56 ` Alexei Starovoitov 2018-01-20 16:56 ` [kernel-hardening] " Alexei Starovoitov 2018-01-20 16:56 ` Alexei Starovoitov 2018-01-20 17:07 ` Alexei Starovoitov 2018-01-20 17:07 ` [kernel-hardening] " Alexei Starovoitov 2018-01-20 17:07 ` Alexei Starovoitov
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