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Message-ID: <tip-e836673c9b4966bc78e38aeda25f7022c57f0e90@git.kernel.org>
Date: Tue, 30 Apr 2019 04:13:48 -0700
From: tip-bot for Nadav Amit <tipbot@...or.com>
To: linux-tip-commits@...r.kernel.org
Cc: tglx@...utronix.de, hpa@...or.com, akpm@...ux-foundation.org,
luto@...nel.org, bp@...en8.de, mhiramat@...nel.org,
riel@...riel.com, ard.biesheuvel@...aro.org,
linux-kernel@...r.kernel.org, namit@...are.com,
linux_dti@...oud.com, will.deacon@....com, dave.hansen@...el.com,
kristen@...ux.intel.com, kernel-hardening@...ts.openwall.com,
peterz@...radead.org, rick.p.edgecombe@...el.com, mingo@...nel.org,
keescook@...omium.org, deneen.t.dock@...el.com, jkosina@...e.cz,
torvalds@...ux-foundation.org
Subject: [tip:x86/mm] x86/alternatives: Add text_poke_kgdb() to not assert
the lock when debugging
Commit-ID: e836673c9b4966bc78e38aeda25f7022c57f0e90
Gitweb: https://git.kernel.org/tip/e836673c9b4966bc78e38aeda25f7022c57f0e90
Author: Nadav Amit <namit@...are.com>
AuthorDate: Thu, 25 Apr 2019 17:11:21 -0700
Committer: Ingo Molnar <mingo@...nel.org>
CommitDate: Tue, 30 Apr 2019 12:37:47 +0200
x86/alternatives: Add text_poke_kgdb() to not assert the lock when debugging
text_mutex is currently expected to be held before text_poke() is
called, but 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.
Create 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.
Suggested-by: Peter Zijlstra <peterz@...radead.org>
Signed-off-by: Nadav Amit <namit@...are.com>
Signed-off-by: Rick Edgecombe <rick.p.edgecombe@...el.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@...radead.org>
Reviewed-by: Masami Hiramatsu <mhiramat@...nel.org>
Acked-by: Jiri Kosina <jkosina@...e.cz>
Cc: <akpm@...ux-foundation.org>
Cc: <ard.biesheuvel@...aro.org>
Cc: <deneen.t.dock@...el.com>
Cc: <kernel-hardening@...ts.openwall.com>
Cc: <kristen@...ux.intel.com>
Cc: <linux_dti@...oud.com>
Cc: <will.deacon@....com>
Cc: Andy Lutomirski <luto@...nel.org>
Cc: Borislav Petkov <bp@...en8.de>
Cc: Dave Hansen <dave.hansen@...el.com>
Cc: H. Peter Anvin <hpa@...or.com>
Cc: Kees Cook <keescook@...omium.org>
Cc: Linus Torvalds <torvalds@...ux-foundation.org>
Cc: Rik van Riel <riel@...riel.com>
Cc: Thomas Gleixner <tglx@...utronix.de>
Fixes: 9222f606506c ("x86/alternatives: Lockdep-enforce text_mutex in text_poke*()")
Link: https://lkml.kernel.org/r/20190426001143.4983-2-namit@vmware.com
Signed-off-by: Ingo Molnar <mingo@...nel.org>
---
arch/x86/include/asm/text-patching.h | 1 +
arch/x86/kernel/alternative.c | 52 ++++++++++++++++++++++++++----------
arch/x86/kernel/kgdb.c | 11 ++++----
3 files changed, 45 insertions(+), 19 deletions(-)
diff --git a/arch/x86/include/asm/text-patching.h b/arch/x86/include/asm/text-patching.h
index e85ff65c43c3..f8fc8e86cf01 100644
--- a/arch/x86/include/asm/text-patching.h
+++ b/arch/x86/include/asm/text-patching.h
@@ -35,6 +35,7 @@ extern void *text_poke_early(void *addr, const void *opcode, size_t len);
* inconsistent instruction while you patch.
*/
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.c b/arch/x86/kernel/alternative.c
index 9a79c7808f9c..0a814d73547a 100644
--- a/arch/x86/kernel/alternative.c
+++ b/arch/x86/kernel/alternative.c
@@ -679,18 +679,7 @@ 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 void *__text_poke(void *addr, const void *opcode, size_t len)
{
unsigned long flags;
char *vaddr;
@@ -703,8 +692,6 @@ 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);
@@ -733,6 +720,43 @@ void *text_poke(void *addr, const void *opcode, size_t len)
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)
+{
+ 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.
+ * 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.
+ */
+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.c b/arch/x86/kernel/kgdb.c
index 4ff6b4cdb941..2b203ee5b879 100644
--- a/arch/x86/kernel/kgdb.c
+++ b/arch/x86/kernel/kgdb.c
@@ -759,13 +759,13 @@ 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.
*/
if (mutex_is_locked(&text_mutex))
return -EBUSY;
- text_poke((void *)bpt->bpt_addr, arch_kgdb_ops.gdb_bpt_instr,
- BREAK_INSTR_SIZE);
+ text_poke_kgdb((void *)bpt->bpt_addr, arch_kgdb_ops.gdb_bpt_instr,
+ BREAK_INSTR_SIZE);
err = probe_kernel_read(opc, (char *)bpt->bpt_addr, BREAK_INSTR_SIZE);
if (err)
return err;
@@ -784,12 +784,13 @@ 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);
+ text_poke_kgdb((void *)bpt->bpt_addr, bpt->saved_instr,
+ BREAK_INSTR_SIZE);
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;
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