From: Peter Zijlstra <peterz@infradead.org>
To: Kees Cook <keescook@chromium.org>
Cc: "Reshetova, Elena" <elena.reshetova@intel.com>,
Greg KH <gregkh@linuxfoundation.org>,
Arnd Bergmann <arnd@arndb.de>,
Thomas Gleixner <tglx@linutronix.de>,
Ingo Molnar <mingo@kernel.org>,
"H. Peter Anvin" <h.peter.anvin@intel.com>,
Will Deacon <will.deacon@arm.com>,
David Windsor <dwindsor@gmail.com>,
Hans Liljestrand <ishkamiel@gmail.com>,
David Howells <dhowells@redhat.com>,
LKML <linux-kernel@vger.kernel.org>,
"kernel-hardening@lists.openwall.com"
<kernel-hardening@lists.openwall.com>
Subject: Re: [PATCH 4/4] refcount: Report failures through CHECK_DATA_CORRUPTION
Date: Mon, 6 Feb 2017 09:57:39 +0100 [thread overview]
Message-ID: <20170206085739.GH6515@twins.programming.kicks-ass.net> (raw)
In-Reply-To: <CAGXu5jLvpq6B80aN44JCOfHrov5LKX1_9r4aWb7LNM7pAW_SEQ@mail.gmail.com>
On Sun, Feb 05, 2017 at 03:33:36PM -0800, Kees Cook wrote:
> On Sun, Feb 5, 2017 at 7:40 AM, Peter Zijlstra <peterz@infradead.org> wrote:
> > On Fri, Feb 03, 2017 at 03:26:52PM -0800, Kees Cook wrote:
> >> This converts from WARN_ON() to CHECK_DATA_CORRUPTION() in the
> >> CONFIG_DEBUG_REFCOUNT case. Additionally moves refcount_t sanity check
> >> conditionals into regular function flow. Since CHECK_DATA_CORRUPTION()
> >> is marked __much_check, we override few cases where the failure has
> >> already been handled but we want to explicitly report it.
> >>
> >> Signed-off-by: Kees Cook <keescook@chromium.org>
> >> ---
> >> include/linux/refcount.h | 35 ++++++++++++++++++++++-------------
> >> lib/Kconfig.debug | 2 ++
> >> 2 files changed, 24 insertions(+), 13 deletions(-)
> >>
> >> diff --git a/include/linux/refcount.h b/include/linux/refcount.h
> >> index 5b89cad62237..ef32910c7dd8 100644
> >> --- a/include/linux/refcount.h
> >> +++ b/include/linux/refcount.h
> >> @@ -43,10 +43,10 @@
> >> #include <linux/spinlock.h>
> >>
> >> #if CONFIG_DEBUG_REFCOUNT
> >> -#define REFCOUNT_WARN(cond, str) WARN_ON(cond)
> >> +#define REFCOUNT_CHECK(cond, str) CHECK_DATA_CORRUPTION(cond, str)
> >
> > OK, so that goes back to a full WARN() which will make the generated
> > code gigantic due to the whole printk() trainwreck :/
>
> Hrm, perhaps we need three levels? WARN_ON, WARN, and BUG?
Did consider that, didn't really know if that made sense.
Like I wrote, ideally we'd end up using something like the x86 exception
table with a custom handler. Just no idea how to pull that off without
doing a full blown arch specific implementation, so I didn't go there
quite yet.
That way refcount_inc() would end up being inlined to something like:
mov 0x148(%rdi),%eax
jmp 2f
1: lock cmpxchg %edx,0x148(%rdi)
je 4f
2: lea -0x1(%rax),%ecx
lea 0x1(%rax),%edx
cmp $0xfffffffd,%ecx
jbe 1b
3: ud2
4:
_ASM_EXTABLE_HANDLE(3b, 4b, ex_handler_refcount_inc)
where:
bool ex_handler_refcount_inc(const struct exception_table_entry *fixup,
struct pt_regs *regs, int trapnr)
{
regs->ip = ex_fixup_addr(fixup);
if (!regs->ax)
WARN(1, "refcount_t: increment on 0; use-after-free.\n");
else
WARN(1, "refcount_t: saturated; leaking memory.\n");
return true;
}
and the handler is shared between all instances and can be as big and
fancy as we'd like.
WARNING: multiple messages have this Message-ID (diff)
From: Peter Zijlstra <peterz@infradead.org>
To: Kees Cook <keescook@chromium.org>
Cc: "Reshetova, Elena" <elena.reshetova@intel.com>,
Greg KH <gregkh@linuxfoundation.org>,
Arnd Bergmann <arnd@arndb.de>,
Thomas Gleixner <tglx@linutronix.de>,
Ingo Molnar <mingo@kernel.org>,
"H. Peter Anvin" <h.peter.anvin@intel.com>,
Will Deacon <will.deacon@arm.com>,
David Windsor <dwindsor@gmail.com>,
Hans Liljestrand <ishkamiel@gmail.com>,
David Howells <dhowells@redhat.com>,
LKML <linux-kernel@vger.kernel.org>,
"kernel-hardening@lists.openwall.com"
<kernel-hardening@lists.openwall.com>
Subject: [kernel-hardening] Re: [PATCH 4/4] refcount: Report failures through CHECK_DATA_CORRUPTION
Date: Mon, 6 Feb 2017 09:57:39 +0100 [thread overview]
Message-ID: <20170206085739.GH6515@twins.programming.kicks-ass.net> (raw)
In-Reply-To: <CAGXu5jLvpq6B80aN44JCOfHrov5LKX1_9r4aWb7LNM7pAW_SEQ@mail.gmail.com>
On Sun, Feb 05, 2017 at 03:33:36PM -0800, Kees Cook wrote:
> On Sun, Feb 5, 2017 at 7:40 AM, Peter Zijlstra <peterz@infradead.org> wrote:
> > On Fri, Feb 03, 2017 at 03:26:52PM -0800, Kees Cook wrote:
> >> This converts from WARN_ON() to CHECK_DATA_CORRUPTION() in the
> >> CONFIG_DEBUG_REFCOUNT case. Additionally moves refcount_t sanity check
> >> conditionals into regular function flow. Since CHECK_DATA_CORRUPTION()
> >> is marked __much_check, we override few cases where the failure has
> >> already been handled but we want to explicitly report it.
> >>
> >> Signed-off-by: Kees Cook <keescook@chromium.org>
> >> ---
> >> include/linux/refcount.h | 35 ++++++++++++++++++++++-------------
> >> lib/Kconfig.debug | 2 ++
> >> 2 files changed, 24 insertions(+), 13 deletions(-)
> >>
> >> diff --git a/include/linux/refcount.h b/include/linux/refcount.h
> >> index 5b89cad62237..ef32910c7dd8 100644
> >> --- a/include/linux/refcount.h
> >> +++ b/include/linux/refcount.h
> >> @@ -43,10 +43,10 @@
> >> #include <linux/spinlock.h>
> >>
> >> #if CONFIG_DEBUG_REFCOUNT
> >> -#define REFCOUNT_WARN(cond, str) WARN_ON(cond)
> >> +#define REFCOUNT_CHECK(cond, str) CHECK_DATA_CORRUPTION(cond, str)
> >
> > OK, so that goes back to a full WARN() which will make the generated
> > code gigantic due to the whole printk() trainwreck :/
>
> Hrm, perhaps we need three levels? WARN_ON, WARN, and BUG?
Did consider that, didn't really know if that made sense.
Like I wrote, ideally we'd end up using something like the x86 exception
table with a custom handler. Just no idea how to pull that off without
doing a full blown arch specific implementation, so I didn't go there
quite yet.
That way refcount_inc() would end up being inlined to something like:
mov 0x148(%rdi),%eax
jmp 2f
1: lock cmpxchg %edx,0x148(%rdi)
je 4f
2: lea -0x1(%rax),%ecx
lea 0x1(%rax),%edx
cmp $0xfffffffd,%ecx
jbe 1b
3: ud2
4:
_ASM_EXTABLE_HANDLE(3b, 4b, ex_handler_refcount_inc)
where:
bool ex_handler_refcount_inc(const struct exception_table_entry *fixup,
struct pt_regs *regs, int trapnr)
{
regs->ip = ex_fixup_addr(fixup);
if (!regs->ax)
WARN(1, "refcount_t: increment on 0; use-after-free.\n");
else
WARN(1, "refcount_t: saturated; leaking memory.\n");
return true;
}
and the handler is shared between all instances and can be as big and
fancy as we'd like.
next prev parent reply other threads:[~2017-02-06 8:57 UTC|newest]
Thread overview: 47+ messages / expand[flat|nested] mbox.gz Atom feed top
2017-02-03 23:26 [PATCH 0/4] refcount_t followups Kees Cook
2017-02-03 23:26 ` [kernel-hardening] " Kees Cook
2017-02-03 23:26 ` [PATCH 1/4] refcount_t: fix Kconfig help Kees Cook
2017-02-03 23:26 ` [kernel-hardening] " Kees Cook
2017-02-03 23:26 ` [PATCH 2/4] lkdtm: convert to refcount_t testing Kees Cook
2017-02-03 23:26 ` [kernel-hardening] " Kees Cook
2017-02-10 8:32 ` [tip:locking/core] lkdtm: Convert " tip-bot for Kees Cook
2017-02-03 23:26 ` [PATCH 3/4] bug: Switch data corruption check to __must_check Kees Cook
2017-02-03 23:26 ` [kernel-hardening] " Kees Cook
2017-02-03 23:26 ` [PATCH 4/4] refcount: Report failures through CHECK_DATA_CORRUPTION Kees Cook
2017-02-03 23:26 ` [kernel-hardening] " Kees Cook
2017-02-05 15:40 ` Peter Zijlstra
2017-02-05 15:40 ` [kernel-hardening] " Peter Zijlstra
2017-02-05 23:33 ` Kees Cook
2017-02-05 23:33 ` [kernel-hardening] " Kees Cook
2017-02-06 8:57 ` Peter Zijlstra [this message]
2017-02-06 8:57 ` Peter Zijlstra
2017-02-06 16:54 ` Kees Cook
2017-02-06 16:54 ` [kernel-hardening] " Kees Cook
2017-02-07 8:34 ` Peter Zijlstra
2017-02-07 8:34 ` [kernel-hardening] " Peter Zijlstra
2017-02-07 11:10 ` Mark Rutland
2017-02-07 11:10 ` Mark Rutland
2017-02-07 12:36 ` Peter Zijlstra
2017-02-07 12:36 ` Peter Zijlstra
2017-02-07 13:50 ` Mark Rutland
2017-02-07 13:50 ` Mark Rutland
2017-02-07 15:07 ` Peter Zijlstra
2017-02-07 15:07 ` Peter Zijlstra
2017-02-07 16:03 ` Mark Rutland
2017-02-07 16:03 ` Mark Rutland
2017-02-07 17:30 ` Peter Zijlstra
2017-02-07 17:30 ` Peter Zijlstra
2017-02-07 17:55 ` Mark Rutland
2017-02-07 17:55 ` Mark Rutland
2017-02-08 9:12 ` Peter Zijlstra
2017-02-08 9:12 ` Peter Zijlstra
2017-02-08 9:43 ` Peter Zijlstra
2017-02-08 9:43 ` Peter Zijlstra
2017-02-08 14:10 ` Mark Rutland
2017-02-08 14:10 ` Mark Rutland
2017-02-08 21:20 ` Kees Cook
2017-02-08 21:20 ` Kees Cook
2017-02-09 10:27 ` Peter Zijlstra
2017-02-09 10:27 ` Peter Zijlstra
2017-02-10 23:39 ` Kees Cook
2017-02-10 23:39 ` Kees Cook
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