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Bug in kalign_heap #16

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ankarenko opened this issue Oct 9, 2023 · 1 comment
Open

Bug in kalign_heap #16

ankarenko opened this issue Oct 9, 2023 · 1 comment

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@ankarenko
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Hello, thanks for the project, it very helps me to learn os development

I've found a little but quite severe bug in kalign_heap function

mos/src/kernel/memory/malloc.c

Line 156 in 8327ee4

while (!last->next)

I think it should be
while (last->next)
@ankarenko
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ankarenko commented Oct 19, 2023 •
edited
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mos/src/kernel/memory/vmm.c

Lines 171 to 175 in 8327ee4

char *aligned_object = kalign_heap(PMM_FRAME_SIZE);
// NOTE: MQ 2019-11-24 page directory, page table have to be aligned by 4096
struct pdirectory *va_dir = kcalloc(1, sizeof(struct pdirectory));
if (aligned_object)
kfree(aligned_object);

Also this code might return badly aligned address because kcallloc may choose one of free blocks in a list of kblocklist instead of allocating the new properly aligned one by kalign_heap function

To test it, you can put before the code

void* ptr = kcalloc(PMM_FRAME_SIZE, 1);  // make sure ptr is not properly aligned
kfree(ptr);

... kalign code ...  

// struct pdirectory *va_dir will be equal to ptr which is not properly aligned

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@ankarenko