On 09.08.21 20:30, Sascha Hauer wrote:
> On Thu, Aug 05, 2021 at 04:06:42PM +0200, Ahmad Fatoum wrote:
>> On 03.08.21 11:44, Rouven Czerwinski wrote:
>>> Use the information from the reserved memory entries to modify the
>>> mapping of memory regions to mark them as uncachable and not-executable.
>>> This also prevents the processor from speculating into these regions,
>>> preventing hard to debug scenarios where boots fail for unknown reasons.
>>>
>>> Signed-off-by: Rouven Czerwinski <r.czerwinski@xxxxxxxxxxxxxx>
>>> ---
>>> arch/arm/cpu/mmu.c | 34 ++++++++++++++++++++++++++++++++--
>>> 1 file changed, 32 insertions(+), 2 deletions(-)
>>>
>>> diff --git a/arch/arm/cpu/mmu.c b/arch/arm/cpu/mmu.c
>>> index 6388e1bf14..73f4cf5b36 100644
>>> --- a/arch/arm/cpu/mmu.c
>>> +++ b/arch/arm/cpu/mmu.c
>>> @@ -17,6 +17,7 @@
>>> #include <memory.h>
>>> #include <asm/system_info.h>
>>> #include <asm/sections.h>
>>> +#include <of.h>
>>>
>>> #include "mmu.h"
>>>
>>> @@ -407,6 +408,36 @@ static void vectors_init(void)
>>> create_vector_table(ARM_LOW_VECTORS);
>>> }
>>>
>>> +static void create_sections_with_intersect(struct memory_bank *bank)
>>> +{
>>> + struct of_reserve_map *res_map;
>>> + unsigned long j_end;
>>> + unsigned long end;
>>> + unsigned long j;
>>> + u32 pmd_flags;
>>> + int i;
>>> +
>>> + res_map = of_get_reserve_map();
>>> + if (!res_map)
>>> + return;
>>
>> If there is no reserve map, you should still map the banks cached.
>> So this early exit is wrong.
>>
>>> +
>>> + end = bank->start + bank->size - 1;
>>> +
>>> + for (j = bank->start; j < end; j += PGDIR_SIZE) {
>>> + pmd_flags = PMD_SECT_DEF_CACHED;
>>> + j_end = j + PGDIR_SIZE - 1;
>>> +
>>> + for (i = 0; i < res_map->num_entries; i++) {
>>> + if ((BIT(i) & res_map->xn) &&
>>> + j_end >= res_map->start[i] &&
>>> + j_end <= res_map->end[i])
>>> + pmd_flags = PMD_SECT_DEF_UNCACHED | PMD_SECT_XN;
>>> + }
>>> +
>>> + create_sections(ttb, j, j_end, pmd_flags);
>>> + }
>>
>> Do we need the nested loop? Can't we create sections cached first
>> and then iterate once over the reserved map, deduce the sections containing
>> start and end and map those uncached?
>
> Wouldn't that open a window to speculate into the areas we want to avoid
> speculating into in the first place?
Right. Forgot that MMU is enabled here.
>
> Sascha
>
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