Re: [PATCH v2 09/18] mips: use simpler access_ok()

Thomas Bogendoerfer
2022-02-21T13:24:56Z

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.

--
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good idea. [ RFC1925, 2.3 ]