From: Christophe Leroy <christophe.leroy@csgroup.eu>
To: Andrew Donnellan <ajd@linux.ibm.com>,
"linuxppc-dev@lists.ozlabs.org" <linuxppc-dev@lists.ozlabs.org>
Cc: Nick Piggin <npiggin@gmail.com>,
"linux-hardening@vger.kernel.org"
<linux-hardening@vger.kernel.org>,
"cmr@bluescreens.de" <cmr@bluescreens.de>
Subject: Re: [RFC PATCH 2/6] powerpc/64s: Helpers to switch between linear and vmapped stack pointers
Date: Sat, 5 Nov 2022 20:28:27 +0100 [thread overview]
Message-ID: <d224142a-cdbf-9eca-b357-1f9862b22cae@csgroup.eu> (raw)
In-Reply-To: <20c79a09-0b95-bb52-2495-999d2365308d@csgroup.eu>
Le 05/11/2022 à 09:00, Christophe Leroy a écrit :
>
>
> Le 04/11/2022 à 18:27, Andrew Donnellan a écrit :
>> powerpc unfortunately has too many places where we run stuff in real mode.
>>
>> With CONFIG_VMAP_STACK enabled, this means we need to be able to swap the
>> stack pointer to use the linear mapping when we enter a real mode section,
>> and back afterwards.
>>
>> Store the top bits of the stack pointer in both the linear map and the
>> vmalloc space in the PACA, and add some helper macros/functions to swap
>> between them.
>
> That may work when pagesize is 64k because stack is on a single page,
> but I doubt is works with 4k pages, because vmalloc may allocate non
> contiguous pages.
>
[snip]
>
>> +
>> +#else // __ASSEMBLY__
>> +
>> +#include <asm/paca.h>
>> +#include <asm/reg.h>
>> +#include <linux/mm.h>
>> +
>> +#define stack_pa(ptr) (is_vmalloc_addr((ptr)) ? (void *)vmalloc_to_phys((void *)(ptr)) : (void *)ptr)
>> +
>> +static __always_inline void swap_stack_linear(void)
>> +{
>> + current_stack_pointer = get_paca()->kstack_linear_base | \
>> + (current_stack_pointer & (THREAD_SIZE - 1));
>
> That looks hacky. I think you can't just change current_stack_pointer on
> the fly. You have to provide something similar to call_do_softirq() or
> call_do_irq()
>
Maybe you can have a look at Nic's RFC for calling functions in real
mode :
https://patchwork.ozlabs.org/project/linuxppc-dev/patch/20210212012041.392566-1-npiggin@gmail.com/
Christophe
next prev parent reply other threads:[~2022-11-05 19:29 UTC|newest]
Thread overview: 17+ messages / expand[flat|nested] mbox.gz Atom feed top
2022-11-04 17:27 [RFC PATCH 0/6] VMAP_STACK support for book3s64 Andrew Donnellan
2022-11-04 17:27 ` [RFC PATCH 1/6] powerpc/64s: Fix assembly to support larger values of THREAD_SIZE Andrew Donnellan
2022-11-04 17:51 ` Christophe Leroy
2023-04-26 7:03 ` Andrew Donnellan
2022-11-04 17:27 ` [RFC PATCH 2/6] powerpc/64s: Helpers to switch between linear and vmapped stack pointers Andrew Donnellan
2022-11-05 8:00 ` Christophe Leroy
2022-11-05 19:28 ` Christophe Leroy [this message]
2022-11-07 12:38 ` Nicholas Piggin
2022-11-04 17:27 ` [RFC PATCH 3/6] powerpc/powernv: Keep MSR in register across OPAL entry/return path Andrew Donnellan
2022-11-04 18:00 ` Christophe Leroy
2022-11-04 17:27 ` [RFC PATCH 4/6] powerpc/powernv: Convert pointers to physical addresses in OPAL call args Andrew Donnellan
2022-11-07 0:00 ` Russell Currey
2022-11-08 16:21 ` Christophe Leroy
2022-11-04 17:27 ` [RFC PATCH 5/6] powerpc/powernv/idle: Convert stack pointer to physical address Andrew Donnellan
2022-11-08 16:17 ` Christophe Leroy
2022-11-04 17:27 ` [RFC PATCH 6/6] powerpc/64s: Enable CONFIG_VMAP_STACK Andrew Donnellan
2022-11-05 17:07 ` Christophe Leroy
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