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131484c8da
So the dwarf2 annotations in low level assembly code have become an increasing hindrance: unreadable, messy macros mixed into some of the most security sensitive code paths of the Linux kernel. These debug info annotations don't even buy the upstream kernel anything: dwarf driven stack unwinding has caused problems in the past so it's out of tree, and the upstream kernel only uses the much more robust framepointers based stack unwinding method. In addition to that there's a steady, slow bitrot going on with these annotations, requiring frequent fixups. There's no tooling and no functionality upstream that keeps it correct. So burn down the sick forest, allowing new, healthier growth: 27 files changed, 350 insertions(+), 1101 deletions(-) Someone who has the willingness and time to do this properly can attempt to reintroduce dwarf debuginfo in x86 assembly code plus dwarf unwinding from first principles, with the following conditions: - it should be maximally readable, and maximally low-key to 'ordinary' code reading and maintenance. - find a build time method to insert dwarf annotations automatically in the most common cases, for pop/push instructions that manipulate the stack pointer. This could be done for example via a preprocessing step that just looks for common patterns - plus special annotations for the few cases where we want to depart from the default. We have hundreds of CFI annotations, so automating most of that makes sense. - it should come with build tooling checks that ensure that CFI annotations are sensible. We've seen such efforts from the framepointer side, and there's no reason it couldn't be done on the dwarf side. Cc: Andy Lutomirski <luto@amacapital.net> Cc: Borislav Petkov <bp@alien8.de> Cc: Brian Gerst <brgerst@gmail.com> Cc: Denys Vlasenko <dvlasenk@redhat.com> Cc: Frédéric Weisbecker <fweisbec@gmail.com Cc: H. Peter Anvin <hpa@zytor.com> Cc: Jan Beulich <JBeulich@suse.com> Cc: Josh Poimboeuf <jpoimboe@redhat.com> Cc: Linus Torvalds <torvalds@linux-foundation.org> Cc: Peter Zijlstra <peterz@infradead.org> Cc: Thomas Gleixner <tglx@linutronix.de> Cc: linux-kernel@vger.kernel.org Signed-off-by: Ingo Molnar <mingo@kernel.org>
128 lines
2.4 KiB
ArmAsm
128 lines
2.4 KiB
ArmAsm
/*
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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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.text
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ENTRY(__get_user_1)
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GET_THREAD_INFO(%_ASM_DX)
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cmp TI_addr_limit(%_ASM_DX),%_ASM_AX
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jae bad_get_user
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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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ENTRY(__get_user_2)
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add $1,%_ASM_AX
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jc bad_get_user
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GET_THREAD_INFO(%_ASM_DX)
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cmp TI_addr_limit(%_ASM_DX),%_ASM_AX
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jae bad_get_user
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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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ENTRY(__get_user_4)
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add $3,%_ASM_AX
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jc bad_get_user
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GET_THREAD_INFO(%_ASM_DX)
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cmp TI_addr_limit(%_ASM_DX),%_ASM_AX
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jae bad_get_user
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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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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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GET_THREAD_INFO(%_ASM_DX)
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cmp TI_addr_limit(%_ASM_DX),%_ASM_AX
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jae bad_get_user
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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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GET_THREAD_INFO(%_ASM_DX)
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cmp TI_addr_limit(%_ASM_DX),%_ASM_AX
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jae bad_get_user_8
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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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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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