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From: Nadav Amit <namit@vmware.com>
To: Ingo Molnar <mingo@redhat.com>
Cc: <linux-kernel@vger.kernel.org>, <x86@kernel.org>,
	"H. Peter Anvin" <hpa@zytor.com>,
	Thomas Gleixner <tglx@linutronix.de>,
	Borislav Petkov <bp@alien8.de>,
	Dave Hansen <dave.hansen@linux.intel.com>,
	Nadav Amit <namit@vmware.com>, Jiri Kosina <jkosina@suse.cz>,
	Andy Lutomirski <luto@kernel.org>,
	Kees Cook <keescook@chromium.org>,
	Dave Hansen <dave.hansen@intel.com>
Subject: [PATCH v3 1/7] Fix "x86/alternatives: Lockdep-enforce text_mutex in text_poke*()"
Date: Fri, 2 Nov 2018 16:29:40 -0700	[thread overview]
Message-ID: <20181102232946.98461-2-namit@vmware.com> (raw)
In-Reply-To: <20181102232946.98461-1-namit@vmware.com>

text_mutex is expected to be held before text_poke() is called, but we
cannot add a lockdep assertion since kgdb does not take it, 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.

Add a comment to clarify this behavior, and restore the assertions as
they were before the recent commit.

This partially reverts commit 9222f606506c ("x86/alternatives:
Lockdep-enforce text_mutex in text_poke*()")

Cc: Jiri Kosina <jkosina@suse.cz>
Cc: Andy Lutomirski <luto@kernel.org>
Cc: Kees Cook <keescook@chromium.org>
Cc: Dave Hansen <dave.hansen@intel.com>
Fixes: 9222f606506c ("x86/alternatives: Lockdep-enforce text_mutex in text_poke*()")
Reviewed-by: Masami Hiramatsu <mhiramat@kernel.org>
Tested-by: Masami Hiramatsu <mhiramat@kernel.org>
Suggested-by: Peter Zijlstra <peterz@infradead.org>
Signed-off-by: Nadav Amit <namit@vmware.com>
---
 arch/x86/kernel/alternative.c | 7 +++++--
 1 file changed, 5 insertions(+), 2 deletions(-)

diff --git a/arch/x86/kernel/alternative.c b/arch/x86/kernel/alternative.c
index ebeac487a20c..1511d96d2e69 100644
--- a/arch/x86/kernel/alternative.c
+++ b/arch/x86/kernel/alternative.c
@@ -688,6 +688,11 @@ void *__init_or_module text_poke_early(void *addr, const void *opcode,
  * 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: Must be called under text_mutex. kgdb is an exception: it does not
+ *	    hold the mutex, as it *supposedly* ensures that no other core is
+ *	    holding the mutex and ensures that none of them will acquire the
+ *	    mutex while the code runs.
  */
 void *text_poke(void *addr, const void *opcode, size_t len)
 {
@@ -702,8 +707,6 @@ 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);
-- 
2.17.1


  reply	other threads:[~2018-11-02 23:31 UTC|newest]

Thread overview: 30+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2018-11-02 23:29 [PATCH v3 0/7] x86/alternatives: text_poke() fixes Nadav Amit
2018-11-02 23:29 ` Nadav Amit [this message]
2018-11-03 10:11   ` [PATCH v3 1/7] Fix "x86/alternatives: Lockdep-enforce text_mutex in text_poke*()" Jiri Kosina
2018-11-04 20:58   ` Thomas Gleixner
2018-11-05 18:14     ` Nadav Amit
2018-11-02 23:29 ` [PATCH v3 2/7] x86/jump_label: Use text_poke_early() during early_init Nadav Amit
2018-11-05 12:39   ` Peter Zijlstra
2018-11-05 13:33     ` Peter Zijlstra
2018-11-05 14:09   ` Peter Zijlstra
2018-11-05 17:22     ` Andy Lutomirski
2018-11-05 17:49       ` Nadav Amit
2018-11-05 19:03         ` Andy Lutomirski
2018-11-05 19:25           ` Nadav Amit
2018-11-05 20:05             ` Andy Lutomirski
2018-11-05 20:28               ` Thomas Gleixner
2018-11-05 21:31                 ` Nadav Amit
2018-11-07 19:13     ` Nadav Amit
2018-11-08 10:41       ` Peter Zijlstra
2018-11-02 23:29 ` [PATCH v3 3/7] x86/mm: temporary mm struct Nadav Amit
2018-11-02 23:29 ` [PATCH v3 4/7] fork: provide a function for copying init_mm Nadav Amit
2018-11-02 23:29 ` [PATCH v3 5/7] x86/alternatives: initializing temporary mm for patching Nadav Amit
2018-11-02 23:29 ` [PATCH v3 6/7] x86/alternatives: use temporary mm for text poking Nadav Amit
2018-11-05 13:19   ` Peter Zijlstra
2018-11-05 13:30   ` Peter Zijlstra
2018-11-05 18:04     ` Nadav Amit
2018-11-06  8:20       ` Peter Zijlstra
2018-11-06 13:11         ` Peter Zijlstra
2018-11-06 18:11           ` Nadav Amit
2018-11-06 19:08             ` Peter Zijlstra
2018-11-02 23:29 ` [PATCH v3 7/7] x86/alternatives: remove text_poke() return value Nadav Amit

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