linux-kernel - Re: [PATCH v2 09/18] mips: use simpler access

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 for Android: free password hash cracker in your pocket

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Date:   Mon, 21 Feb 2022 14:24:56 +0100
From:   Thomas Bogendoerfer <tsbogend@...ha.franken.de>
To:     Arnd Bergmann <arnd@...nel.org>
Cc:     Linus Torvalds <torvalds@...ux-foundation.org>,
        Christoph Hellwig <hch@....de>, linux-arch@...r.kernel.org,
        linux-mm@...ck.org, linux-api@...r.kernel.org, arnd@...db.de,
        linux-kernel@...r.kernel.org, viro@...iv.linux.org.uk,
        linux@...linux.org.uk, will@...nel.org, guoren@...nel.org,
        bcain@...eaurora.org, geert@...ux-m68k.org, monstr@...str.eu,
        nickhu@...estech.com, green.hu@...il.com, dinguyen@...nel.org,
        shorne@...il.com, deller@....de, mpe@...erman.id.au,
        peterz@...radead.org, mingo@...hat.com, mark.rutland@....com,
        hca@...ux.ibm.com, dalias@...c.org, davem@...emloft.net,
        richard@....at, x86@...nel.org, jcmvbkbc@...il.com,
        ebiederm@...ssion.com, akpm@...ux-foundation.org, ardb@...nel.org,
        linux-alpha@...r.kernel.org, linux-snps-arc@...ts.infradead.org,
        linux-csky@...r.kernel.org, linux-hexagon@...r.kernel.org,
        linux-ia64@...r.kernel.org, linux-m68k@...ts.linux-m68k.org,
        linux-mips@...r.kernel.org, openrisc@...ts.librecores.org,
        linux-parisc@...r.kernel.org, linuxppc-dev@...ts.ozlabs.org,
        linux-riscv@...ts.infradead.org, linux-s390@...r.kernel.org,
        linux-sh@...r.kernel.org, sparclinux@...r.kernel.org,
        linux-um@...ts.infradead.org, linux-xtensa@...ux-xtensa.org
Subject: Re: [PATCH v2 09/18] mips: use simpler access_ok()

On Wed, Feb 16, 2022 at 02:13:23PM +0100, Arnd Bergmann wrote:
> 
> diff --git a/arch/mips/include/asm/uaccess.h b/arch/mips/include/asm/uaccess.h
> index db9a8e002b62..d7c89dc3426c 100644
> --- a/arch/mips/include/asm/uaccess.h
> +++ b/arch/mips/include/asm/uaccess.h
> @@ -19,6 +19,7 @@
>  #ifdef CONFIG_32BIT
>  
>  #define __UA_LIMIT 0x80000000UL
> +#define TASK_SIZE_MAX	__UA_LIMIT
>  
>  #define __UA_ADDR	".word"
>  #define __UA_LA		"la"
> @@ -33,6 +34,7 @@
>  extern u64 __ua_limit;
>  
>  #define __UA_LIMIT	__ua_limit
> +#define TASK_SIZE_MAX	XKSSEG

this doesn't work. For every access above maximum implemented virtual address
space of the CPU an address error will be issued, but not a TLB miss.
And address error isn't able to handle this situation.

With this patch

diff --git a/arch/mips/kernel/unaligned.c b/arch/mips/kernel/unaligned.c
index df4b708c04a9..3911f1481f3d 100644
--- a/arch/mips/kernel/unaligned.c
+++ b/arch/mips/kernel/unaligned.c
@@ -1480,6 +1480,13 @@ asmlinkage void do_ade(struct pt_regs *regs)
 	prev_state = exception_enter();
 	perf_sw_event(PERF_COUNT_SW_ALIGNMENT_FAULTS,
 			1, regs, regs->cp0_badvaddr);
+
+	/* Are we prepared to handle this kernel fault?	 */
+	if (fixup_exception(regs)) {
+		current->thread.cp0_baduaddr = regs->cp0_badvaddr;
+		return;
+	}
+
 	/*
 	 * Did we catch a fault trying to load an instruction?
 	 */

I at least get my simple test cases fixed, but I'm not sure this is
correct.

Is there a reason to not also #define TASK_SIZE_MAX   __UA_LIMIT like
for the 32bit case ?

Thomas.

-- 
Crap can work. Given enough thrust pigs will fly, but it's not necessarily a
good idea.                                                [ RFC1925, 2.3 ]