c7f631cb07
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, i.e.
array_index_nospec(). 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>
Signed-off-by: Dan Williams <dan.j.williams@intel.com>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Cc: linux-arch@vger.kernel.org
Cc: Kees Cook <keescook@chromium.org>
Cc: kernel-hardening@lists.openwall.com
Cc: gregkh@linuxfoundation.org
Cc: Al Viro <viro@zeniv.linux.org.uk>
Cc: Andy Lutomirski <luto@kernel.org>
Cc: torvalds@linux-foundation.org
Cc: alan@linux.intel.com
Link: https://lkml.kernel.org/r/151727417469.33451.11804043010080838495.stgit@dwillia2-desk3.amr.corp.intel.com
144 lines
3 KiB
ArmAsm
144 lines
3 KiB
ArmAsm
/* SPDX-License-Identifier: GPL-2.0 */
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/*
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* __get_user functions.
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*
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* (C) Copyright 1998 Linus Torvalds
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* (C) Copyright 2005 Andi Kleen
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* (C) Copyright 2008 Glauber Costa
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*
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* These functions have a non-standard call interface
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* to make them more efficient, especially as they
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* return an error value in addition to the "real"
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* return value.
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*/
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/*
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* __get_user_X
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*
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* Inputs: %[r|e]ax contains the address.
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*
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* Outputs: %[r|e]ax is error code (0 or -EFAULT)
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* %[r|e]dx contains zero-extended value
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* %ecx contains the high half for 32-bit __get_user_8
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*
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*
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* These functions should not modify any other registers,
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* as they get called from within inline assembly.
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*/
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#include <linux/linkage.h>
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#include <asm/page_types.h>
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#include <asm/errno.h>
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#include <asm/asm-offsets.h>
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#include <asm/thread_info.h>
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#include <asm/asm.h>
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#include <asm/smap.h>
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#include <asm/export.h>
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.text
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ENTRY(__get_user_1)
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mov PER_CPU_VAR(current_task), %_ASM_DX
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cmp TASK_addr_limit(%_ASM_DX),%_ASM_AX
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jae bad_get_user
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sbb %_ASM_DX, %_ASM_DX /* array_index_mask_nospec() */
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and %_ASM_DX, %_ASM_AX
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ASM_STAC
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1: movzbl (%_ASM_AX),%edx
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xor %eax,%eax
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ASM_CLAC
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ret
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ENDPROC(__get_user_1)
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EXPORT_SYMBOL(__get_user_1)
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ENTRY(__get_user_2)
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add $1,%_ASM_AX
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jc bad_get_user
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mov PER_CPU_VAR(current_task), %_ASM_DX
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cmp TASK_addr_limit(%_ASM_DX),%_ASM_AX
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jae bad_get_user
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sbb %_ASM_DX, %_ASM_DX /* array_index_mask_nospec() */
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and %_ASM_DX, %_ASM_AX
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ASM_STAC
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2: movzwl -1(%_ASM_AX),%edx
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xor %eax,%eax
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ASM_CLAC
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ret
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ENDPROC(__get_user_2)
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EXPORT_SYMBOL(__get_user_2)
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ENTRY(__get_user_4)
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add $3,%_ASM_AX
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jc bad_get_user
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mov PER_CPU_VAR(current_task), %_ASM_DX
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cmp TASK_addr_limit(%_ASM_DX),%_ASM_AX
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jae bad_get_user
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sbb %_ASM_DX, %_ASM_DX /* array_index_mask_nospec() */
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and %_ASM_DX, %_ASM_AX
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ASM_STAC
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3: movl -3(%_ASM_AX),%edx
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xor %eax,%eax
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ASM_CLAC
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ret
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ENDPROC(__get_user_4)
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EXPORT_SYMBOL(__get_user_4)
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ENTRY(__get_user_8)
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#ifdef CONFIG_X86_64
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add $7,%_ASM_AX
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jc bad_get_user
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mov PER_CPU_VAR(current_task), %_ASM_DX
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cmp TASK_addr_limit(%_ASM_DX),%_ASM_AX
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jae bad_get_user
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sbb %_ASM_DX, %_ASM_DX /* array_index_mask_nospec() */
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and %_ASM_DX, %_ASM_AX
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ASM_STAC
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4: movq -7(%_ASM_AX),%rdx
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xor %eax,%eax
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ASM_CLAC
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ret
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#else
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add $7,%_ASM_AX
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jc bad_get_user_8
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mov PER_CPU_VAR(current_task), %_ASM_DX
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cmp TASK_addr_limit(%_ASM_DX),%_ASM_AX
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jae bad_get_user_8
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sbb %_ASM_DX, %_ASM_DX /* array_index_mask_nospec() */
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and %_ASM_DX, %_ASM_AX
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ASM_STAC
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4: movl -7(%_ASM_AX),%edx
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5: movl -3(%_ASM_AX),%ecx
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xor %eax,%eax
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ASM_CLAC
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ret
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#endif
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ENDPROC(__get_user_8)
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EXPORT_SYMBOL(__get_user_8)
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bad_get_user:
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xor %edx,%edx
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mov $(-EFAULT),%_ASM_AX
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ASM_CLAC
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ret
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END(bad_get_user)
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#ifdef CONFIG_X86_32
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bad_get_user_8:
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xor %edx,%edx
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xor %ecx,%ecx
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mov $(-EFAULT),%_ASM_AX
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ASM_CLAC
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ret
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END(bad_get_user_8)
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#endif
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_ASM_EXTABLE(1b,bad_get_user)
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_ASM_EXTABLE(2b,bad_get_user)
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_ASM_EXTABLE(3b,bad_get_user)
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#ifdef CONFIG_X86_64
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_ASM_EXTABLE(4b,bad_get_user)
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#else
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_ASM_EXTABLE(4b,bad_get_user_8)
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_ASM_EXTABLE(5b,bad_get_user_8)
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#endif
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