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Peter Anvin" , Thomas Gleixner , Borislav Petkov , Dave Hansen , Nadav Amit , Jiri Kosina , Andy Lutomirski , Kees Cook , Dave Hansen , Masami Hiramatsu Subject: [PATCH v4 01/10] Fix "x86/alternatives: Lockdep-enforce text_mutex in text_poke*()" Date: Sat, 10 Nov 2018 15:17:23 -0800 Message-ID: <20181110231732.15060-2-namit@vmware.com> X-Mailer: git-send-email 2.17.1 In-Reply-To: <20181110231732.15060-1-namit@vmware.com> References: <20181110231732.15060-1-namit@vmware.com> MIME-Version: 1.0 Content-Type: text/plain Received-SPF: None (EX13-EDG-OU-001.vmware.com: namit@vmware.com does not designate permitted sender hosts) Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org 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. 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. This patch creates two wrapper functions, text_poke() and text_poke_kgdb() which do or do not run the lockdep assertion respectively. While we are at it, change the return code of text_poke() to something meaningful. One day, callers might actually respect it and the existing BUG_ON() when patching fails could be removed. For kgdb, the return value can actually be used. Cc: Jiri Kosina 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 Signed-off-by: Nadav Amit --- arch/x86/include/asm/text-patching.h | 3 +- arch/x86/kernel/alternative.c | 72 +++++++++++++++++++++------- arch/x86/kernel/kgdb.c | 15 ++++-- 3 files changed, 66 insertions(+), 24 deletions(-) diff --git a/arch/x86/include/asm/text-patching.h b/arch/x86/include/asm/text-patching.h index e85ff65c43c3..5a2600370763 100644 --- a/arch/x86/include/asm/text-patching.h +++ b/arch/x86/include/asm/text-patching.h @@ -34,7 +34,8 @@ extern void *text_poke_early(void *addr, const void *opcode, size_t len); * On the local CPU you need to be protected again NMI or MCE handlers seeing an * inconsistent instruction while you patch. */ -extern void *text_poke(void *addr, const void *opcode, size_t len); +extern int text_poke(void *addr, const void *opcode, size_t len); +extern int 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.c b/arch/x86/kernel/alternative.c index ebeac487a20c..ebe9210dc92e 100644 --- a/arch/x86/kernel/alternative.c +++ b/arch/x86/kernel/alternative.c @@ -678,23 +678,12 @@ void *__init_or_module text_poke_early(void *addr, const void *opcode, return addr; } -/** - * 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. - * It means the size must be writable atomically and the address must be aligned - * in a way that permits an atomic write. It also makes sure we fit on a single - * page. - */ -void *text_poke(void *addr, const void *opcode, size_t len) +static int __text_poke(void *addr, const void *opcode, size_t len) { unsigned long flags; char *vaddr; struct page *pages[2]; - int i; + int i, r = 0; /* * While boot memory allocator is runnig we cannot use struct @@ -702,8 +691,6 @@ void *text_poke(void *addr, const void *opcode, size_t len) */ BUG_ON(!after_bootmem); - lockdep_assert_held(&text_mutex); - if (!core_kernel_text((unsigned long)addr)) { pages[0] = vmalloc_to_page(addr); pages[1] = vmalloc_to_page(addr + PAGE_SIZE); @@ -712,7 +699,8 @@ void *text_poke(void *addr, const void *opcode, size_t len) WARN_ON(!PageReserved(pages[0])); pages[1] = virt_to_page(addr + PAGE_SIZE); } - BUG_ON(!pages[0]); + if (!pages[0]) + return -EFAULT; local_irq_save(flags); set_fixmap(FIX_TEXT_POKE0, page_to_phys(pages[0])); if (pages[1]) @@ -727,9 +715,57 @@ void *text_poke(void *addr, const void *opcode, size_t len) /* Could also do a CLFLUSH here to speed up CPU recovery; but that causes hangs on some VIA CPUs. */ for (i = 0; i < len; i++) - BUG_ON(((char *)addr)[i] != ((char *)opcode)[i]); + if (((char *)addr)[i] != ((char *)opcode)[i]) + r = -EFAULT; local_irq_restore(flags); - return addr; + return r; +} + +/** + * 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. + * It means the size must be writable atomically and the address must be aligned + * in a way that permits an atomic write. It also makes sure we fit on a single + * page. + */ +int text_poke(void *addr, const void *opcode, size_t len) +{ + int r; + + lockdep_assert_held(&text_mutex); + + r = __text_poke(addr, opcode, len); + + /* + * TODO: change the callers to consider the return value and remove this + * historical assertion. + */ + BUG_ON(r); + + return r; +} + +/** + * 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. + * It means the size must be writable atomically and the address must be aligned + * in a way that permits an atomic write. It also makes sure we fit on a single + * page. + * + * Context: should only be used by kgdb, which ensures no other core is running, + * despite the fact it does not hold the text_mutex. + */ +int text_poke_kgdb(void *addr, const void *opcode, size_t len) +{ + return __text_poke(addr, opcode, len); } static void do_sync_core(void *info) diff --git a/arch/x86/kernel/kgdb.c b/arch/x86/kernel/kgdb.c index 8e36f249646e..8091b2e381d4 100644 --- a/arch/x86/kernel/kgdb.c +++ b/arch/x86/kernel/kgdb.c @@ -763,13 +763,15 @@ 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. */ if (mutex_is_locked(&text_mutex)) return -EBUSY; - text_poke((void *)bpt->bpt_addr, arch_kgdb_ops.gdb_bpt_instr, - BREAK_INSTR_SIZE); + err = text_poke_kgdb((void *)bpt->bpt_addr, arch_kgdb_ops.gdb_bpt_instr, + BREAK_INSTR_SIZE); + if (err) + return err; err = probe_kernel_read(opc, (char *)bpt->bpt_addr, BREAK_INSTR_SIZE); if (err) return err; @@ -788,12 +790,15 @@ int kgdb_arch_remove_breakpoint(struct kgdb_bkpt *bpt) if (bpt->type != 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. */ if (mutex_is_locked(&text_mutex)) goto knl_write; - text_poke((void *)bpt->bpt_addr, bpt->saved_instr, BREAK_INSTR_SIZE); + err = text_poke_kgdb((void *)bpt->bpt_addr, bpt->saved_instr, + BREAK_INSTR_SIZE); + if (err) + return err; err = probe_kernel_read(opc, (char *)bpt->bpt_addr, BREAK_INSTR_SIZE); if (err || memcmp(opc, bpt->saved_instr, BREAK_INSTR_SIZE)) goto knl_write; -- 2.17.1