linux-kernel - Re: [PATCH] arm64: uprobes: Optimize cache flushes for xol slot

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] [day] [month] [year] [list]

Message-ID: <20240920173223.GA20847@redhat.com>
Date: Fri, 20 Sep 2024 19:32:23 +0200
From: Oleg Nesterov <oleg@...hat.com>
To: Catalin Marinas <catalin.marinas@....com>
Cc: "Liao, Chang" <liaochang1@...wei.com>, mhiramat@...nel.org,
	peterz@...radead.org, will@...nel.org, mark.rutland@....com,
	linux-kernel@...r.kernel.org, linux-trace-kernel@...r.kernel.org,
	linux-arm-kernel@...ts.infradead.org
Subject: Re: [PATCH] arm64: uprobes: Optimize cache flushes for xol slot

On 09/20, Catalin Marinas wrote:
>
> On Fri, Sep 20, 2024 at 04:58:31PM +0800, Liao, Chang wrote:
> >
> >
> > 在 2024/9/19 22:18, Oleg Nesterov 写道:
> > > On 09/19, Liao Chang wrote:
> > >>
> > >> --- a/arch/arm64/kernel/probes/uprobes.c
> > >> +++ b/arch/arm64/kernel/probes/uprobes.c
> > >> @@ -17,12 +17,16 @@ void arch_uprobe_copy_ixol(struct page *page, unsigned long vaddr,
> > >>  	void *xol_page_kaddr = kmap_atomic(page);
> > >>  	void *dst = xol_page_kaddr + (vaddr & ~PAGE_MASK);
> > >>
> > >> +	if (!memcmp(dst, src, len))
> > >> +		goto done;
> > >
> > > can't really comment, I know nothing about arm64...
> > >
> > > but don't we need to change __create_xol_area()
> > >
> > > 	-	area->page = alloc_page(GFP_HIGHUSER);
> > > 	+	area->page = alloc_page(GFP_HIGHUSER | __GFP_ZERO);
> > >
> > > to avoid the false positives?
> >
> > Indeed, it would be safer.
> >
> > Could we tolerate these false positives? Even if the page are not reset
> > to zero bits, if the existing bits are the same as the instruction being
> > copied, it still can execute the correct instruction.
>
> Not if the I-cache has stale data. If alloc_page() returns a page with
> some random data that resembles a valid instruction but there was never
> a cache flush (sync_icache_aliases() on arm64), it's irrelevant whether
> the compare (on the D-cache side) succeeds or not.

But shouldn't the page fault paths on arm64 flush I-cache ?

If alloc_page() returns a page with some random data that resembles a valid
instruction, user-space can't execute this instruction until
special_mapping_fault() installs the page allocated in __create_xol_area().

Again, I know nothing about arm64/icache/etc, I am just curious and trying
to understand...

Oleg.