[BISECTED] kexec regression on PowerBook G4

[LEROY Christophe]

Aaro Koskinen <aaro.koskinen at iki.fi> a écrit :

> Hi,
>
> On Wed, May 22, 2019 at 07:44:56AM +0000, Christophe Leroy wrote:
>> On 05/22/2019 06:14 AM, Christophe Leroy wrote:
>> >Le 22/05/2019 à 00:18, Aaro Koskinen a écrit :
>> >>I was trying to upgrade from v5.0 -> v5.1 on PowerBook G4, but when
>> >>trying
>> >>to kexec a kernel the system gets stuck (no errors seen on the console).
>> >
>> >Do you mean you are trying to kexec a v5.1 kernel from a v5.0 kernel, or
>> >do you have a working v5.1 kernel, but kexec doesn't work with it ?
>> >
>> >>
>> >>Bisected to: 93c4a162b014 ("powerpc/6xx: Store PGDIR physical address
>> >>in a SPRG"). This commit doesn't revert cleanly anymore but I tested
>> >>that the one before works OK.
>> >
>> >Not sure that's the problem. There was a problem with that commit, but it
>> >was fixed by 4622a2d43101 ("powerpc/6xx: fix setup and use of
>> >SPRN_SPRG_PGDIR for hash32").
>> >You probably hit some commit between those two during bisect, that's
>> >likely the reason why you ended here.
>> >
>> >Can you restart your bisect from 4622a2d43101 ?
>> >
>> >If you have CONFIG_SMP, maybe you should also consider taking 397d2300b08c
>> >("powerpc/32s: fix flush_hash_pages() on SMP"). Stable 5.1.4 includes it.
>> >
>> >>
>> >>With current Linus HEAD (9c7db5004280), it gets a bit further but still
>> >>doesn't work: now I get an error on the console after kexec "Starting
>> >>new kernel! ... Bye!":
>> >>
>> >>    kernel tried to execute exec-protected page (...) - exploit attempt?
>> >
>> >Interesting.
>> >
>> >Do you have CONFIG_STRICT_KERNEL_RWX=y in your .config ? If so, can you
>> >retry without it ?
>>
>> After looking at the code, I don't thing CONFIG_STRICT_KERNEL_RWX will make
>> any difference. Can you try the patch below ?
>
> Doesn't help (git refuses the patch as corrupted, so I had to do those
> changes manually, but I'm pretty sure I got it right).
>
> I still get the "kernel tried to execute exec-protected page...". What
> should I try next?

Can you provide full details of the Oops you get ? And also your System.map ?
K
Also build with CONFIG_PPC_PTDUMP and mount /sys/kernel/debug and give  
content of /sys/kernel/debug/powerpc/block_address_translation and  
.../segment_registers before the failing kexec, and also  
/sys/kernel/debug/kernel_page_tables

Thx
Christophe

>
> A.
>
>> From 8c1039da0d0f26cdf995156a905fc97fe7bda36c Mon Sep 17 00:00:00 2001
>> From: Christophe Leroy <christophe.leroy at c-s.fr>
>> Date: Wed, 22 May 2019 07:28:42 +0000
>> Subject: [PATCH] Fix Kexec
>>
>> ---
>>  arch/powerpc/include/asm/pgtable.h     | 2 ++
>>  arch/powerpc/kernel/machine_kexec_32.c | 4 ++++
>>  arch/powerpc/mm/pgtable_32.c           | 2 +-
>>  3 files changed, 7 insertions(+), 1 deletion(-)
>>
>> diff --git a/arch/powerpc/include/asm/pgtable.h
>> b/arch/powerpc/include/asm/pgtable.h
>> index 3f53be60fb01..642eea937229 100644
>> --- a/arch/powerpc/include/asm/pgtable.h
>> +++ b/arch/powerpc/include/asm/pgtable.h
>> @@ -140,6 +140,8 @@ static inline void pte_frag_set(mm_context_t *ctx, void
>> *p)
>>  }
>>  #endif
>>
>> +int change_page_attr(struct page *page, int numpages, pgprot_t prot);
>> +
>>  #endif /* __ASSEMBLY__ */
>>
>>  #endif /* _ASM_POWERPC_PGTABLE_H */
>> diff --git a/arch/powerpc/kernel/machine_kexec_32.c
>> b/arch/powerpc/kernel/machine_kexec_32.c
>> index affe5dcce7f4..4f719501e6ae 100644
>> --- a/arch/powerpc/kernel/machine_kexec_32.c
>> +++ b/arch/powerpc/kernel/machine_kexec_32.c
>> @@ -54,6 +54,10 @@ void default_machine_kexec(struct kimage *image)
>>  	memcpy((void *)reboot_code_buffer, relocate_new_kernel,
>>  						relocate_new_kernel_size);
>>
>> +	change_page_attr(image->control_code_page,
>> +			 ALIGN(KEXEC_CONTROL_PAGE_SIZE, PAGE_SIZE) >> PAGE_SHIFT,
>> +			 PAGE_KERNEL_TEXT);
>> +
>>  	flush_icache_range(reboot_code_buffer,
>>  				reboot_code_buffer + KEXEC_CONTROL_PAGE_SIZE);
>>  	printk(KERN_INFO "Bye!\n");
>> diff --git a/arch/powerpc/mm/pgtable_32.c b/arch/powerpc/mm/pgtable_32.c
>> index 16ada373b32b..0e4651d803fc 100644
>> --- a/arch/powerpc/mm/pgtable_32.c
>> +++ b/arch/powerpc/mm/pgtable_32.c
>> @@ -340,7 +340,7 @@ static int __change_page_attr_noflush(struct page *page,
>> pgprot_t prot)
>>   *
>>   * THIS DOES NOTHING WITH BAT MAPPINGS, DEBUG USE ONLY
>>   */
>> -static int change_page_attr(struct page *page, int numpages, pgprot_t prot)
>> +int change_page_attr(struct page *page, int numpages, pgprot_t prot)
>>  {
>>  	int i, err = 0;
>>  	unsigned long flags;
>> --
>> 2.13.3