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x86/debug: Remove perpetually broken, unmaintainable dwarf annotations
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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>
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Ingo Molnar committed Jun 2, 2015
1 parent cdeb604 commit 131484c
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Showing 27 changed files with 350 additions and 1,101 deletions.
10 changes: 2 additions & 8 deletions arch/x86/Makefile
View file
Original file line number Diff line number Diff line change
Expand Up @@ -149,21 +149,15 @@ endif
sp-$(CONFIG_X86_32) := esp
sp-$(CONFIG_X86_64) := rsp

# do binutils support CFI?
cfi := $(call as-instr,.cfi_startproc\n.cfi_rel_offset $(sp-y)$(comma)0\n.cfi_endproc,-DCONFIG_AS_CFI=1)
# is .cfi_signal_frame supported too?
cfi-sigframe := $(call as-instr,.cfi_startproc\n.cfi_signal_frame\n.cfi_endproc,-DCONFIG_AS_CFI_SIGNAL_FRAME=1)
cfi-sections := $(call as-instr,.cfi_sections .debug_frame,-DCONFIG_AS_CFI_SECTIONS=1)

# does binutils support specific instructions?
asinstr := $(call as-instr,fxsaveq (%rax),-DCONFIG_AS_FXSAVEQ=1)
asinstr += $(call as-instr,pshufb %xmm0$(comma)%xmm0,-DCONFIG_AS_SSSE3=1)
asinstr += $(call as-instr,crc32l %eax$(comma)%eax,-DCONFIG_AS_CRC32=1)
avx_instr := $(call as-instr,vxorps %ymm0$(comma)%ymm1$(comma)%ymm2,-DCONFIG_AS_AVX=1)
avx2_instr :=$(call as-instr,vpbroadcastb %xmm0$(comma)%ymm1,-DCONFIG_AS_AVX2=1)

KBUILD_AFLAGS += $(cfi) $(cfi-sigframe) $(cfi-sections) $(asinstr) $(avx_instr) $(avx2_instr)
KBUILD_CFLAGS += $(cfi) $(cfi-sigframe) $(cfi-sections) $(asinstr) $(avx_instr) $(avx2_instr)
KBUILD_AFLAGS += $(asinstr) $(avx_instr) $(avx2_instr)
KBUILD_CFLAGS += $(asinstr) $(avx_instr) $(avx2_instr)

LDFLAGS := -m elf_$(UTS_MACHINE)

Expand Down
133 changes: 32 additions & 101 deletions arch/x86/ia32/ia32entry.S
View file
Original file line number Diff line number Diff line change
Expand Up @@ -4,7 +4,6 @@
* Copyright 2000-2002 Andi Kleen, SuSE Labs.
*/

#include <asm/dwarf2.h>
#include <asm/calling.h>
#include <asm/asm-offsets.h>
#include <asm/current.h>
Expand Down Expand Up @@ -60,17 +59,6 @@
movl %eax,%eax /* zero extension */
.endm

.macro CFI_STARTPROC32 simple
CFI_STARTPROC \simple
CFI_UNDEFINED r8
CFI_UNDEFINED r9
CFI_UNDEFINED r10
CFI_UNDEFINED r11
CFI_UNDEFINED r12
CFI_UNDEFINED r13
CFI_UNDEFINED r14
CFI_UNDEFINED r15
.endm

#ifdef CONFIG_PARAVIRT
ENTRY(native_usergs_sysret32)
Expand Down Expand Up @@ -102,11 +90,6 @@ ENDPROC(native_usergs_sysret32)
* with the int 0x80 path.
*/
ENTRY(ia32_sysenter_target)
CFI_STARTPROC32 simple
CFI_SIGNAL_FRAME
CFI_DEF_CFA rsp,0
CFI_REGISTER rsp,rbp

/*
* Interrupts are off on entry.
* We do not frame this tiny irq-off block with TRACE_IRQS_OFF/ON,
Expand All @@ -121,25 +104,21 @@ ENTRY(ia32_sysenter_target)
movl %eax, %eax

movl ASM_THREAD_INFO(TI_sysenter_return, %rsp, 0), %r10d
CFI_REGISTER rip,r10

/* Construct struct pt_regs on stack */
pushq_cfi $__USER32_DS /* pt_regs->ss */
pushq_cfi %rbp /* pt_regs->sp */
CFI_REL_OFFSET rsp,0
pushfq_cfi /* pt_regs->flags */
pushq_cfi $__USER32_CS /* pt_regs->cs */
pushq_cfi %r10 /* pt_regs->ip = thread_info->sysenter_return */
CFI_REL_OFFSET rip,0
pushq_cfi_reg rax /* pt_regs->orig_ax */
pushq_cfi_reg rdi /* pt_regs->di */
pushq_cfi_reg rsi /* pt_regs->si */
pushq_cfi_reg rdx /* pt_regs->dx */
pushq_cfi_reg rcx /* pt_regs->cx */
pushq_cfi $-ENOSYS /* pt_regs->ax */
pushq $__USER32_DS /* pt_regs->ss */
pushq %rbp /* pt_regs->sp */
pushfq /* pt_regs->flags */
pushq $__USER32_CS /* pt_regs->cs */
pushq %r10 /* pt_regs->ip = thread_info->sysenter_return */
pushq %rax /* pt_regs->orig_ax */
pushq %rdi /* pt_regs->di */
pushq %rsi /* pt_regs->si */
pushq %rdx /* pt_regs->dx */
pushq %rcx /* pt_regs->cx */
pushq $-ENOSYS /* pt_regs->ax */
cld
sub $(10*8),%rsp /* pt_regs->r8-11,bp,bx,r12-15 not saved */
CFI_ADJUST_CFA_OFFSET 10*8

/*
* no need to do an access_ok check here because rbp has been
Expand All @@ -161,8 +140,8 @@ sysenter_flags_fixed:

orl $TS_COMPAT, ASM_THREAD_INFO(TI_status, %rsp, SIZEOF_PTREGS)
testl $_TIF_WORK_SYSCALL_ENTRY, ASM_THREAD_INFO(TI_flags, %rsp, SIZEOF_PTREGS)
CFI_REMEMBER_STATE
jnz sysenter_tracesys

sysenter_do_call:
/* 32bit syscall -> 64bit C ABI argument conversion */
movl %edi,%r8d /* arg5 */
Expand Down Expand Up @@ -193,14 +172,12 @@ sysexit_from_sys_call:
*/
andl $~TS_COMPAT,ASM_THREAD_INFO(TI_status, %rsp, SIZEOF_PTREGS)
movl RIP(%rsp),%ecx /* User %eip */
CFI_REGISTER rip,rcx
RESTORE_RSI_RDI
xorl %edx,%edx /* avoid info leaks */
xorq %r8,%r8
xorq %r9,%r9
xorq %r10,%r10
movl EFLAGS(%rsp),%r11d /* User eflags */
/*CFI_RESTORE rflags*/
TRACE_IRQS_ON

/*
Expand Down Expand Up @@ -231,8 +208,6 @@ sysexit_from_sys_call:
*/
USERGS_SYSRET32

CFI_RESTORE_STATE

#ifdef CONFIG_AUDITSYSCALL
.macro auditsys_entry_common
movl %esi,%r8d /* 5th arg: 4th syscall arg */
Expand Down Expand Up @@ -282,8 +257,8 @@ sysexit_audit:
#endif

sysenter_fix_flags:
pushq_cfi $(X86_EFLAGS_IF|X86_EFLAGS_FIXED)
popfq_cfi
pushq $(X86_EFLAGS_IF|X86_EFLAGS_FIXED)
popfq
jmp sysenter_flags_fixed

sysenter_tracesys:
Expand All @@ -298,7 +273,6 @@ sysenter_tracesys:
LOAD_ARGS32 /* reload args from stack in case ptrace changed it */
RESTORE_EXTRA_REGS
jmp sysenter_do_call
CFI_ENDPROC
ENDPROC(ia32_sysenter_target)

/*
Expand Down Expand Up @@ -332,43 +306,33 @@ ENDPROC(ia32_sysenter_target)
* with the int 0x80 path.
*/
ENTRY(ia32_cstar_target)
CFI_STARTPROC32 simple
CFI_SIGNAL_FRAME
CFI_DEF_CFA rsp,0
CFI_REGISTER rip,rcx
/*CFI_REGISTER rflags,r11*/

/*
* Interrupts are off on entry.
* We do not frame this tiny irq-off block with TRACE_IRQS_OFF/ON,
* it is too small to ever cause noticeable irq latency.
*/
SWAPGS_UNSAFE_STACK
movl %esp,%r8d
CFI_REGISTER rsp,r8
movq PER_CPU_VAR(cpu_current_top_of_stack),%rsp
ENABLE_INTERRUPTS(CLBR_NONE)

/* Zero-extending 32-bit regs, do not remove */
movl %eax,%eax

/* Construct struct pt_regs on stack */
pushq_cfi $__USER32_DS /* pt_regs->ss */
pushq_cfi %r8 /* pt_regs->sp */
CFI_REL_OFFSET rsp,0
pushq_cfi %r11 /* pt_regs->flags */
pushq_cfi $__USER32_CS /* pt_regs->cs */
pushq_cfi %rcx /* pt_regs->ip */
CFI_REL_OFFSET rip,0
pushq_cfi_reg rax /* pt_regs->orig_ax */
pushq_cfi_reg rdi /* pt_regs->di */
pushq_cfi_reg rsi /* pt_regs->si */
pushq_cfi_reg rdx /* pt_regs->dx */
pushq_cfi_reg rbp /* pt_regs->cx */
pushq $__USER32_DS /* pt_regs->ss */
pushq %r8 /* pt_regs->sp */
pushq %r11 /* pt_regs->flags */
pushq $__USER32_CS /* pt_regs->cs */
pushq %rcx /* pt_regs->ip */
pushq %rax /* pt_regs->orig_ax */
pushq %rdi /* pt_regs->di */
pushq %rsi /* pt_regs->si */
pushq %rdx /* pt_regs->dx */
pushq %rbp /* pt_regs->cx */
movl %ebp,%ecx
pushq_cfi $-ENOSYS /* pt_regs->ax */
pushq $-ENOSYS /* pt_regs->ax */
sub $(10*8),%rsp /* pt_regs->r8-11,bp,bx,r12-15 not saved */
CFI_ADJUST_CFA_OFFSET 10*8

/*
* no need to do an access_ok check here because r8 has been
Expand All @@ -380,8 +344,8 @@ ENTRY(ia32_cstar_target)
ASM_CLAC
orl $TS_COMPAT, ASM_THREAD_INFO(TI_status, %rsp, SIZEOF_PTREGS)
testl $_TIF_WORK_SYSCALL_ENTRY, ASM_THREAD_INFO(TI_flags, %rsp, SIZEOF_PTREGS)
CFI_REMEMBER_STATE
jnz cstar_tracesys

cstar_do_call:
/* 32bit syscall -> 64bit C ABI argument conversion */
movl %edi,%r8d /* arg5 */
Expand All @@ -403,15 +367,12 @@ sysretl_from_sys_call:
andl $~TS_COMPAT, ASM_THREAD_INFO(TI_status, %rsp, SIZEOF_PTREGS)
RESTORE_RSI_RDI_RDX
movl RIP(%rsp),%ecx
CFI_REGISTER rip,rcx
movl EFLAGS(%rsp),%r11d
/*CFI_REGISTER rflags,r11*/
xorq %r10,%r10
xorq %r9,%r9
xorq %r8,%r8
TRACE_IRQS_ON
movl RSP(%rsp),%esp
CFI_RESTORE rsp
/*
* 64bit->32bit SYSRET restores eip from ecx,
* eflags from r11 (but RF and VM bits are forced to 0),
Expand All @@ -430,7 +391,6 @@ sysretl_from_sys_call:

#ifdef CONFIG_AUDITSYSCALL
cstar_auditsys:
CFI_RESTORE_STATE
movl %r9d,R9(%rsp) /* register to be clobbered by call */
auditsys_entry_common
movl R9(%rsp),%r9d /* reload 6th syscall arg */
Expand Down Expand Up @@ -460,7 +420,6 @@ ia32_badarg:
ASM_CLAC
movq $-EFAULT,%rax
jmp ia32_sysret
CFI_ENDPROC

/*
* Emulated IA32 system calls via int 0x80.
Expand All @@ -484,15 +443,6 @@ ia32_badarg:
*/

ENTRY(ia32_syscall)
CFI_STARTPROC32 simple
CFI_SIGNAL_FRAME
CFI_DEF_CFA rsp,5*8
/*CFI_REL_OFFSET ss,4*8 */
CFI_REL_OFFSET rsp,3*8
/*CFI_REL_OFFSET rflags,2*8 */
/*CFI_REL_OFFSET cs,1*8 */
CFI_REL_OFFSET rip,0*8

/*
* Interrupts are off on entry.
* We do not frame this tiny irq-off block with TRACE_IRQS_OFF/ON,
Expand All @@ -506,15 +456,14 @@ ENTRY(ia32_syscall)
movl %eax,%eax

/* Construct struct pt_regs on stack (iret frame is already on stack) */
pushq_cfi_reg rax /* pt_regs->orig_ax */
pushq_cfi_reg rdi /* pt_regs->di */
pushq_cfi_reg rsi /* pt_regs->si */
pushq_cfi_reg rdx /* pt_regs->dx */
pushq_cfi_reg rcx /* pt_regs->cx */
pushq_cfi $-ENOSYS /* pt_regs->ax */
pushq %rax /* pt_regs->orig_ax */
pushq %rdi /* pt_regs->di */
pushq %rsi /* pt_regs->si */
pushq %rdx /* pt_regs->dx */
pushq %rcx /* pt_regs->cx */
pushq $-ENOSYS /* pt_regs->ax */
cld
sub $(10*8),%rsp /* pt_regs->r8-11,bp,bx,r12-15 not saved */
CFI_ADJUST_CFA_OFFSET 10*8

orl $TS_COMPAT, ASM_THREAD_INFO(TI_status, %rsp, SIZEOF_PTREGS)
testl $_TIF_WORK_SYSCALL_ENTRY, ASM_THREAD_INFO(TI_flags, %rsp, SIZEOF_PTREGS)
Expand Down Expand Up @@ -544,7 +493,6 @@ ia32_tracesys:
LOAD_ARGS32 /* reload args from stack in case ptrace changed it */
RESTORE_EXTRA_REGS
jmp ia32_do_call
CFI_ENDPROC
END(ia32_syscall)

.macro PTREGSCALL label, func
Expand All @@ -554,8 +502,6 @@ GLOBAL(\label)
jmp ia32_ptregs_common
.endm

CFI_STARTPROC32

PTREGSCALL stub32_rt_sigreturn, sys32_rt_sigreturn
PTREGSCALL stub32_sigreturn, sys32_sigreturn
PTREGSCALL stub32_fork, sys_fork
Expand All @@ -569,23 +515,8 @@ GLOBAL(stub32_clone)

ALIGN
ia32_ptregs_common:
CFI_ENDPROC
CFI_STARTPROC32 simple
CFI_SIGNAL_FRAME
CFI_DEF_CFA rsp,SIZEOF_PTREGS
CFI_REL_OFFSET rax,RAX
CFI_REL_OFFSET rcx,RCX
CFI_REL_OFFSET rdx,RDX
CFI_REL_OFFSET rsi,RSI
CFI_REL_OFFSET rdi,RDI
CFI_REL_OFFSET rip,RIP
/* CFI_REL_OFFSET cs,CS*/
/* CFI_REL_OFFSET rflags,EFLAGS*/
CFI_REL_OFFSET rsp,RSP
/* CFI_REL_OFFSET ss,SS*/
SAVE_EXTRA_REGS 8
call *%rax
RESTORE_EXTRA_REGS 8
ret
CFI_ENDPROC
END(ia32_ptregs_common)
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