netdev - Re: [PATCH 12/13] x86/jitalloc: prepare to allocate exectuatble memory as ROX

lists.openwall.net		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 linux-cve-announce 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: Thu, 1 Jun 2023 20:50:39 +0000
From: "Edgecombe, Rick P" <rick.p.edgecombe@...el.com>
To: "kent.overstreet@...ux.dev" <kent.overstreet@...ux.dev>
CC: "tglx@...utronix.de" <tglx@...utronix.de>, "mcgrof@...nel.org"
	<mcgrof@...nel.org>, "deller@....de" <deller@....de>,
	"netdev@...r.kernel.org" <netdev@...r.kernel.org>, "davem@...emloft.net"
	<davem@...emloft.net>, "linux@...linux.org.uk" <linux@...linux.org.uk>,
	"linux-mips@...r.kernel.org" <linux-mips@...r.kernel.org>,
	"linuxppc-dev@...ts.ozlabs.org" <linuxppc-dev@...ts.ozlabs.org>,
	"hca@...ux.ibm.com" <hca@...ux.ibm.com>, "catalin.marinas@....com"
	<catalin.marinas@....com>, "linux-kernel@...r.kernel.org"
	<linux-kernel@...r.kernel.org>, "linux-riscv@...ts.infradead.org"
	<linux-riscv@...ts.infradead.org>, "linux-s390@...r.kernel.org"
	<linux-s390@...r.kernel.org>, "palmer@...belt.com" <palmer@...belt.com>,
	"chenhuacai@...nel.org" <chenhuacai@...nel.org>, "mpe@...erman.id.au"
	<mpe@...erman.id.au>, "x86@...nel.org" <x86@...nel.org>,
	"tsbogend@...ha.franken.de" <tsbogend@...ha.franken.de>, "rppt@...nel.org"
	<rppt@...nel.org>, "linux-trace-kernel@...r.kernel.org"
	<linux-trace-kernel@...r.kernel.org>, "linux-parisc@...r.kernel.org"
	<linux-parisc@...r.kernel.org>, "christophe.leroy@...roup.eu"
	<christophe.leroy@...roup.eu>, "rostedt@...dmis.org" <rostedt@...dmis.org>,
	"will@...nel.org" <will@...nel.org>, "dinguyen@...nel.org"
	<dinguyen@...nel.org>, "naveen.n.rao@...ux.ibm.com"
	<naveen.n.rao@...ux.ibm.com>, "sparclinux@...r.kernel.org"
	<sparclinux@...r.kernel.org>, "linux-modules@...r.kernel.org"
	<linux-modules@...r.kernel.org>, "bpf@...r.kernel.org" <bpf@...r.kernel.org>,
	"linux-arm-kernel@...ts.infradead.org"
	<linux-arm-kernel@...ts.infradead.org>, "song@...nel.org" <song@...nel.org>,
	"linux-mm@...ck.org" <linux-mm@...ck.org>, "loongarch@...ts.linux.dev"
	<loongarch@...ts.linux.dev>, "akpm@...ux-foundation.org"
	<akpm@...ux-foundation.org>
Subject: Re: [PATCH 12/13] x86/jitalloc: prepare to allocate exectuatble
 memory as ROX

On Thu, 2023-06-01 at 14:38 -0400, Kent Overstreet wrote:
> On Thu, Jun 01, 2023 at 06:13:44PM +0000, Edgecombe, Rick P wrote:
> > > text_poke() _does_ create a separate RW mapping.
> > 
> > Sorry, I meant a separate RW allocation.
> 
> Ah yes, that makes sense
> 
> 
> > 
> > > 
> > > The thing that sucks about text_poke() is that it always does a
> > > full
> > > TLB
> > > flush, and AFAICT that's not remotely needed. What it really
> > > wants to
> > > be
> > > doing is conceptually just
> > > 
> > > kmap_local()
> > > mempcy()
> > > kunmap_loca()
> > > flush_icache();
> > > 
> > > ...except that kmap_local() won't actually create a new mapping
> > > on
> > > non-highmem architectures, so text_poke() open codes it.
> > 
> > Text poke creates only a local CPU RW mapping. It's more secure
> > because
> > other threads can't write to it.
> 
> *nod*, same as kmap_local

It's only used and flushed locally, but it is accessible to all CPU's,
right?

> 
> > It also only needs to flush the local core when it's done since
> > it's
> > not using a shared MM.
>  
> Ahh! Thanks for that; perhaps the comment in text_poke() about IPIs
> could be a bit clearer.
> 
> What is it (if anything) you don't like about text_poke() then? It
> looks
> like it's doing broadly similar things to kmap_local(), so should be
> in the same ballpark from a performance POV?

The way text_poke() is used here, it is creating a new writable alias
and flushing it for *each* write to the module (like for each write of
an individual relocation, etc). I was just thinking it might warrant
some batching or something.