From mboxrd@z Thu Jan 1 00:00:00 1970 Date: Thu, 17 Jan 2019 13:15:54 -0800 In-Reply-To: <20190117154701.78aa8e9d0130716e0d9ac026@kernel.org> References: <20190117003259.23141-1-rick.p.edgecombe@intel.com> <20190117003259.23141-2-rick.p.edgecombe@intel.com> <20190117154701.78aa8e9d0130716e0d9ac026@kernel.org> 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: Masami Hiramatsu , Rick Edgecombe Cc: Andy Lutomirski , Ingo Molnar , linux-kernel@vger.kernel.org, x86@kernel.org, Thomas Gleixner , Borislav Petkov , Nadav Amit , Dave Hansen , Peter Zijlstra , linux_dti@icloud.com, linux-integrity@vger.kernel.org, linux-security-module@vger.kernel.org, akpm@linux-foundation.org, kernel-hardening@lists.openwall.com, linux-mm@kvack.org, will.deacon@arm.com, ard.biesheuvel@linaro.org, kristen@linux.intel.com, deneen.t.dock@intel.com, Nadav Amit , Kees Cook , Dave Hansen List-ID: On January 16, 2019 10:47:01 PM PST, Masami Hiramatsu wrote: >On Wed, 16 Jan 2019 16:32:43 -0800 >Rick Edgecombe wrote: > >> 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 > >Looks good to me=2E > >Reviewed-by: Masami Hiramatsu > >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't= 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 --=20 Sent from my Android device with K-9 Mail=2E Please excuse my brevity=2E