From mboxrd@z Thu Jan 1 00:00:00 1970 Date: Thu, 17 Jan 2019 14:59:09 -0800 In-Reply-To: <8817DE5F-BCF4-4F6A-A496-E0DB6889D86E@vmware.com> References: <20190117003259.23141-1-rick.p.edgecombe@intel.com> <20190117003259.23141-2-rick.p.edgecombe@intel.com> <20190117154701.78aa8e9d0130716e0d9ac026@kernel.org> <8817DE5F-BCF4-4F6A-A496-E0DB6889D86E@vmware.com> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: quoted-printable Subject: Re: [PATCH 01/17] Fix "x86/alternatives: Lockdep-enforce text_mutex in text_poke*()" From: hpa@zytor.com Message-ID: To: Nadav Amit Cc: Masami Hiramatsu , Rick Edgecombe , Andy Lutomirski , Ingo Molnar , LKML , X86 ML , Thomas Gleixner , Borislav Petkov , Dave Hansen , Peter Zijlstra , Damian Tometzki , linux-integrity , LSM List , Andrew Morton , Kernel Hardening , Linux-MM , Will Deacon , Ard Biesheuvel , Kristen Carlson Accardi , "Dock, Deneen T" , Kees Cook , Dave Hansen List-ID: On January 17, 2019 2:39:15 PM PST, Nadav Amit wrote: >> On Jan 17, 2019, at 1:15 PM, hpa@zytor=2Ecom wrote: >>=20 >> On January 16, 2019 10:47:01 PM PST, Masami Hiramatsu > wrote: >>> On Wed, 16 Jan 2019 16:32:43 -0800 >>> Rick Edgecombe wrote: >>>=20 >>>> From: Nadav Amit >>>>=20 >>>> text_mutex is currently expected to be held before text_poke() is >>>> called, but we kgdb does not take the mutex, and instead >*supposedly* >>>> ensures the lock is not taken and will not be acquired by any other >>> core >>>> while text_poke() is running=2E >>>>=20 >>>> The reason for the "supposedly" comment is that it is not entirely >>> clear >>>> that this would be the case if gdb_do_roundup is zero=2E >>>>=20 >>>> This patch creates two wrapper functions, text_poke() and >>>> text_poke_kgdb() which do or do not run the lockdep assertion >>>> respectively=2E >>>>=20 >>>> While we are at it, change the return code of text_poke() to >>> something >>>> meaningful=2E One day, callers might actually respect it and the >>> existing >>>> BUG_ON() when patching fails could be removed=2E For kgdb, the return >>>> value can actually be used=2E >>>=20 >>> Looks good to me=2E >>>=20 >>> Reviewed-by: Masami Hiramatsu >>>=20 >>> Thank you, >>>=20 >>>> Cc: Andy Lutomirski >>>> Cc: Kees Cook >>>> Cc: Dave Hansen >>>> Cc: Masami Hiramatsu >>>> Fixes: 9222f606506c ("x86/alternatives: Lockdep-enforce text_mutex >in >>> text_poke*()") >>>> Suggested-by: Peter Zijlstra >>>> Acked-by: Jiri Kosina >>>> Signed-off-by: Nadav Amit >>>> Signed-off-by: Rick Edgecombe >>>> --- >>>> arch/x86/include/asm/text-patching=2Eh | 1 + >>>> arch/x86/kernel/alternative=2Ec | 52 >>> ++++++++++++++++++++-------- >>>> arch/x86/kernel/kgdb=2Ec | 11 +++--- >>>> 3 files changed, 45 insertions(+), 19 deletions(-) >>>>=20 >>>> diff --git a/arch/x86/include/asm/text-patching=2Eh >>> b/arch/x86/include/asm/text-patching=2Eh >>>> index e85ff65c43c3=2E=2Ef8fc8e86cf01 100644 >>>> --- a/arch/x86/include/asm/text-patching=2Eh >>>> +++ b/arch/x86/include/asm/text-patching=2Eh >>>> @@ -35,6 +35,7 @@ extern void *text_poke_early(void *addr, const >void >>> *opcode, size_t len); >>>> * inconsistent instruction while you patch=2E >>>> */ >>>> extern void *text_poke(void *addr, const void *opcode, size_t len); >>>> +extern void *text_poke_kgdb(void *addr, const void *opcode, size_t >>> len); >>>> extern int poke_int3_handler(struct pt_regs *regs); >>>> extern void *text_poke_bp(void *addr, const void *opcode, size_t >>> len, void *handler); >>>> extern int after_bootmem; >>>> diff --git a/arch/x86/kernel/alternative=2Ec >>> b/arch/x86/kernel/alternative=2Ec >>>> index ebeac487a20c=2E=2Ec6a3a10a2fd5 100644 >>>> --- a/arch/x86/kernel/alternative=2Ec >>>> +++ b/arch/x86/kernel/alternative=2Ec >>>> @@ -678,18 +678,7 @@ void *__init_or_module text_poke_early(void >>> *addr, const void *opcode, >>>> return addr; >>>> } >>>>=20 >>>> -/** >>>> - * text_poke - Update instructions on a live kernel >>>> - * @addr: address to modify >>>> - * @opcode: source of the copy >>>> - * @len: length to copy >>>> - * >>>> - * Only atomic text poke/set should be allowed when not doing >early >>> patching=2E >>>> - * It means the size must be writable atomically and the address >>> must be aligned >>>> - * in a way that permits an atomic write=2E It also makes sure we >fit >>> on a single >>>> - * page=2E >>>> - */ >>>> -void *text_poke(void *addr, const void *opcode, size_t len) >>>> +static void *__text_poke(void *addr, const void *opcode, size_t >len) >>>> { >>>> unsigned long flags; >>>> char *vaddr; >>>> @@ -702,8 +691,6 @@ void *text_poke(void *addr, const void *opcode, >>> size_t len) >>>> */ >>>> BUG_ON(!after_bootmem); >>>>=20 >>>> - lockdep_assert_held(&text_mutex); >>>> - >>>> if (!core_kernel_text((unsigned long)addr)) { >>>> pages[0] =3D vmalloc_to_page(addr); >>>> pages[1] =3D vmalloc_to_page(addr + PAGE_SIZE); >>>> @@ -732,6 +719,43 @@ void *text_poke(void *addr, const void >*opcode, >>> size_t len) >>>> return addr; >>>> } >>>>=20 >>>> +/** >>>> + * text_poke - Update instructions on a live kernel >>>> + * @addr: address to modify >>>> + * @opcode: source of the copy >>>> + * @len: length to copy >>>> + * >>>> + * Only atomic text poke/set should be allowed when not doing >early >>> patching=2E >>>> + * It means the size must be writable atomically and the address >>> must be aligned >>>> + * in a way that permits an atomic write=2E It also makes sure we >fit >>> on a single >>>> + * page=2E >>>> + */ >>>> +void *text_poke(void *addr, const void *opcode, size_t len) >>>> +{ >>>> + lockdep_assert_held(&text_mutex); >>>> + >>>> + return __text_poke(addr, opcode, len); >>>> +} >>>> + >>>> +/** >>>> + * text_poke_kgdb - Update instructions on a live kernel by kgdb >>>> + * @addr: address to modify >>>> + * @opcode: source of the copy >>>> + * @len: length to copy >>>> + * >>>> + * Only atomic text poke/set should be allowed when not doing >early >>> patching=2E >>>> + * It means the size must be writable atomically and the address >>> must be aligned >>>> + * in a way that permits an atomic write=2E It also makes sure we >fit >>> on a single >>>> + * page=2E >>>> + * >>>> + * Context: should only be used by kgdb, which ensures no other >core >>> is running, >>>> + * despite the fact it does not hold the text_mutex=2E >>>> + */ >>>> +void *text_poke_kgdb(void *addr, const void *opcode, size_t len) >>>> +{ >>>> + return __text_poke(addr, opcode, len); >>>> +} >>>> + >>>> static void do_sync_core(void *info) >>>> { >>>> sync_core(); >>>> diff --git a/arch/x86/kernel/kgdb=2Ec b/arch/x86/kernel/kgdb=2Ec >>>> index 5db08425063e=2E=2E1461544cba8b 100644 >>>> --- a/arch/x86/kernel/kgdb=2Ec >>>> +++ b/arch/x86/kernel/kgdb=2Ec >>>> @@ -758,13 +758,13 @@ int kgdb_arch_set_breakpoint(struct kgdb_bkpt >>> *bpt) >>>> if (!err) >>>> return err; >>>> /* >>>> - * It is safe to call text_poke() because normal kernel execution >>>> + * It is safe to call text_poke_kgdb() because normal kernel >>> execution >>>> * is stopped on all cores, so long as the text_mutex is not >>> locked=2E >>>> */ >>>> if (mutex_is_locked(&text_mutex)) >>>> return -EBUSY; >>>> - text_poke((void *)bpt->bpt_addr, arch_kgdb_ops=2Egdb_bpt_instr, >>>> - BREAK_INSTR_SIZE); >>>> + text_poke_kgdb((void *)bpt->bpt_addr, >arch_kgdb_ops=2Egdb_bpt_instr, >>>> + BREAK_INSTR_SIZE); >>>> err =3D probe_kernel_read(opc, (char *)bpt->bpt_addr, >>> BREAK_INSTR_SIZE); >>>> if (err) >>>> return err; >>>> @@ -783,12 +783,13 @@ int kgdb_arch_remove_breakpoint(struct >>> kgdb_bkpt *bpt) >>>> if (bpt->type !=3D BP_POKE_BREAKPOINT) >>>> goto knl_write; >>>> /* >>>> - * It is safe to call text_poke() because normal kernel execution >>>> + * It is safe to call text_poke_kgdb() because normal kernel >>> execution >>>> * is stopped on all cores, so long as the text_mutex is not >>> locked=2E >>>> */ >>>> if (mutex_is_locked(&text_mutex)) >>>> goto knl_write; >>>> - text_poke((void *)bpt->bpt_addr, bpt->saved_instr, >>> BREAK_INSTR_SIZE); >>>> + text_poke_kgdb((void *)bpt->bpt_addr, bpt->saved_instr, >>>> + BREAK_INSTR_SIZE); >>>> err =3D probe_kernel_read(opc, (char *)bpt->bpt_addr, >>> BREAK_INSTR_SIZE); >>>> if (err || memcmp(opc, bpt->saved_instr, BREAK_INSTR_SIZE)) >>>> goto knl_write; >>>> --=20 >>>> 2=2E17=2E1 >>=20 >> If you are reorganizing this code, please do so so that the caller >doesn=E2=80=99t >> have to worry about if it should call text_poke_bp() or >text_poke_early()=2E >> Right now the caller had to know that, which makes no sense=2E > >Did you look at "[11/17] x86/jump-label: remove support for custom >poker=E2=80=9D? > >https://lore=2Ekernel=2Eorg/patchwork/patch/1032857/ > >If this is not what you regard, please be more concrete=2E >text_poke_early() >is still used directly on init and while modules are loaded, which >might not >be great, but is outside of the scope of this patch-set=2E I don't think it is out of scope, although that patch is a huge step in th= e right direction=2E text_poke_{early,bp,=2E=2E=2E}, however, should be fully internal, that is= , static functions, and we should present a single interface, preferably ca= lled text_poke(), to the outside world=2E I think we have three subcases: 1=2E Early, UP, or under stop_machine(); 2=2E Atomic and aligned; 3=2E Breakpoint=2E My proposed algorithm should remove the need for a fixup which should help= this interface, too=2E The specific alignment needed for #2 is started by the hardware people to = be not crossing 16 bytes (NOT a cache line) on any CPU we support SMP on an= d, of course, being possible to do atomically do on the specific CPU (note = that we *can* do a redundantly large store of existing bytes, which adds fl= exibility=2E) To the best of my knowledge any CPU supporting SSE can do an atomic (for o= ur purposes) aligned 16-byte store via MOVAPS; of course any CPU with cx16 = can do it without SSE registers=2E For older CPUs we may be limited to 8-by= te stores (cx8) or even 4-byte stores before we need to use the breakpoint = algorithm=2E --=20 Sent from my Android device with K-9 Mail=2E Please excuse my brevity=2E