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From: tip-bot for Hugh Dickins <tipbot@zytor.com>
To: linux-tip-commits@vger.kernel.org
Cc: akpm@linux-foundation.org, pavel@ucw.cz, jannh@google.com,
	hughd@google.com, dave.hansen@linux.intel.com, x86@kernel.org,
	mingo@redhat.com, rppt@linux.ibm.com, tglx@linutronix.de,
	linux-mm@kvack.org, bp@suse.de, mingo@kernel.org,
	chris@chris-wilson.co.uk, linux-kernel@vger.kernel.org,
	riel@surriel.com, hpa@zytor.com, bigeasy@linutronix.de,
	aarcange@redhat.com
Subject: [tip:x86/urgent] x86/fpu: Use fault_in_pages_writeable() for pre-faulting
Date: Thu, 6 Jun 2019 10:25:18 -0700	[thread overview]
Message-ID: <tip-b81ff1013eb8eef2934ca7e8cf53d553c1029e84@git.kernel.org> (raw)
In-Reply-To: <1557844195-18882-1-git-send-email-rppt@linux.ibm.com>

Commit-ID:  b81ff1013eb8eef2934ca7e8cf53d553c1029e84
Gitweb:     https://git.kernel.org/tip/b81ff1013eb8eef2934ca7e8cf53d553c1029e84
Author:     Hugh Dickins <hughd@google.com>
AuthorDate: Wed, 29 May 2019 09:25:40 +0200
Committer:  Borislav Petkov <bp@suse.de>
CommitDate: Thu, 6 Jun 2019 19:15:17 +0200

x86/fpu: Use fault_in_pages_writeable() for pre-faulting

Since commit

   d9c9ce34ed5c8 ("x86/fpu: Fault-in user stack if copy_fpstate_to_sigframe() fails")

get_user_pages_unlocked() pre-faults user's memory if a write generates
a page fault while the handler is disabled.

This works in general and uncovered a bug as reported by Mike
Rapoport¹. It has been pointed out that this function may be fragile
and a simple pre-fault as in fault_in_pages_writeable() would be a
better solution. Better as in taste and simplicity: that write (as
performed by the alternative function) performs exactly the same
faulting of memory as before. This was suggested by Hugh Dickins and
Andrew Morton.

Use fault_in_pages_writeable() for pre-faulting user's stack.

  [ bigeasy: Write commit message. ]
  [ bp: Massage some. ]

¹ https://lkml.kernel.org/r/1557844195-18882-1-git-send-email-rppt@linux.ibm.com

Fixes: d9c9ce34ed5c8 ("x86/fpu: Fault-in user stack if copy_fpstate_to_sigframe() fails")
Suggested-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Hugh Dickins <hughd@google.com>
Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
Signed-off-by: Borislav Petkov <bp@suse.de>
Tested-by: Chris Wilson <chris@chris-wilson.co.uk>
Cc: Andrea Arcangeli <aarcange@redhat.com>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Dave Hansen <dave.hansen@linux.intel.com>
Cc: "H. Peter Anvin" <hpa@zytor.com>
Cc: Ingo Molnar <mingo@redhat.com>
Cc: Jann Horn <jannh@google.com>
Cc: linux-mm <linux-mm@kvack.org>
Cc: Mike Rapoport <rppt@linux.ibm.com>
Cc: Pavel Machek <pavel@ucw.cz>
Cc: Rik van Riel <riel@surriel.com>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: x86-ml <x86@kernel.org>
Link: https://lkml.kernel.org/r/20190529072540.g46j4kfeae37a3iu@linutronix.de
Link: https://lkml.kernel.org/r/1557844195-18882-1-git-send-email-rppt@linux.ibm.com
---
 arch/x86/kernel/fpu/signal.c | 11 ++---------
 1 file changed, 2 insertions(+), 9 deletions(-)

diff --git a/arch/x86/kernel/fpu/signal.c b/arch/x86/kernel/fpu/signal.c
index 5a8d118bc423..060d6188b453 100644
--- a/arch/x86/kernel/fpu/signal.c
+++ b/arch/x86/kernel/fpu/signal.c
@@ -5,6 +5,7 @@
 
 #include <linux/compat.h>
 #include <linux/cpu.h>
+#include <linux/pagemap.h>
 
 #include <asm/fpu/internal.h>
 #include <asm/fpu/signal.h>
@@ -189,15 +190,7 @@ retry:
 	fpregs_unlock();
 
 	if (ret) {
-		int aligned_size;
-		int nr_pages;
-
-		aligned_size = offset_in_page(buf_fx) + fpu_user_xstate_size;
-		nr_pages = DIV_ROUND_UP(aligned_size, PAGE_SIZE);
-
-		ret = get_user_pages_unlocked((unsigned long)buf_fx, nr_pages,
-					      NULL, FOLL_WRITE);
-		if (ret == nr_pages)
+		if (!fault_in_pages_writeable(buf_fx, fpu_user_xstate_size))
 			goto retry;
 		return -EFAULT;
 	}

  parent reply	other threads:[~2019-06-06 17:26 UTC|newest]

Thread overview: 22+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2019-05-26 17:33 [PATCH] " Sebastian Andrzej Siewior
2019-05-26 17:35 ` Sebastian Andrzej Siewior
2019-05-26 19:25   ` Hugh Dickins
2019-05-28 11:54     ` My emacs problem -- was " Pavel Machek
2019-05-29  4:18 ` Andrew Morton
2019-05-29  7:25   ` [PATCH v2] " Sebastian Andrzej Siewior
2019-05-14 14:29     ` [PATCH] mm/gup: continue VM_FAULT_RETRY processing event for pre-faults Mike Rapoport
2019-05-16 16:25       ` Andrei Vagin
2019-05-21 15:53       ` Mike Rapoport
2019-05-22 19:21       ` Andrew Morton
2019-05-22 19:43         ` Sebastian Andrzej Siewior
2019-05-24 22:22           ` Hugh Dickins
2019-05-25  8:45             ` Sebastian Andrzej Siewior
2019-05-25 18:09               ` Hugh Dickins
2019-05-26 19:36                 ` Sebastian Andrzej Siewior
2019-05-26 20:17                   ` Hugh Dickins
2019-05-26 17:25             ` Pavel Machek
2019-05-22 20:38         ` Mike Rapoport
2019-05-22 21:18           ` Andrew Morton
2019-06-22 17:51             ` Andrea Arcangeli
2019-06-06 17:25       ` tip-bot for Hugh Dickins [this message]
2019-05-29 21:29     ` [PATCH v2] x86/fpu: Use fault_in_pages_writeable() for pre-faulting Chris Wilson

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