lists  /  announce  owl-users  owl-dev  john-users  john-dev  passwdqc-users  yescrypt  popa3d-users  /  oss-security  kernel-hardening  musl  sabotage  tlsify  passwords  /  crypt-dev  xvendor  /  Bugtraq  Full-Disclosure  linux-kernel  linux-netdev  linux-ext4  linux-hardening  PHC 
Open Source and information security mailing list archives
Hash Suite: Windows password security audit tool. GUI, reports in PDF.
[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]
Date:	Wed, 21 May 2014 17:05:41 -0700
From:	Andy Lutomirski <>
To:	Borislav Petkov <>
Cc:	Linus Torvalds <>,
	"Luck, Tony" <>, Jiri Kosina <>,
	Thomas Gleixner <>,
	Steven Rostedt <>,
	Andi Kleen <>,
	"" <>,
	"H. Peter Anvin" <>, Ingo Molnar <>
Subject: Re: [RFC] x86_64: A real proposal for iret-less return to kernel

On Wed, May 21, 2014 at 4:51 PM, Borislav Petkov <> wrote:
> On Thu, May 22, 2014 at 08:30:33AM +0900, Linus Torvalds wrote:
>> If the OS then decides to take down the whole machine, the OS - not
>> the hardware - can choose to do something that will punch through
>> other CPU's NMI blocking (notably, init/reset), but the hardware doing
>> this on its own is just broken if true.
> Not that it is any consolation but MCE is not broadcast on AMD.
> Regardless, exceptions like MCE cannot be held pending and do pierce the
> NMI handler on both.
> Now, if the NMI handler experiences a non-broadcast MCE on the same CPU,
> while running, we're simply going to panic as we're in kernel space
> anyway.
> The only problem is if the NMI handler gets interrupted while running
> on a bystander CPU. And I think we could deal with this because the
> bystander would not see an MCE and will return safely. We just need
> to make sure that it returns back to the said NMI handler and not to
> userspace. Unless I'm missing something ...

Under my "always RET unless returning from IST to weird CS or to
specific known-invalid-stack regions" proposal this should work fine.
In the current code it'll also work fine *unless* it hits really early
in the NMI, in which case a second NMI can kill us.

To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to
More majordomo info at
Please read the FAQ at

Powered by blists - more mailing lists