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https://github.com/AuxXxilium/linux_dsm_epyc7002.git
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773b3e53df
We have powerpc specific logic in our page fault handling to decide if an access to an unmapped address below the stack pointer should expand the stack VMA. The logic aims to prevent userspace from doing bad accesses below the stack pointer. However as long as the stack is < 1MB in size, we allow all accesses without further checks. Adding some debug I see that I can do a full kernel build and LTP run, and not a single process has used more than 1MB of stack. So for the majority of processes the logic never even fires. We also recently found a nasty bug in this code which could cause userspace programs to be killed during signal delivery. It went unnoticed presumably because most processes use < 1MB of stack. The generic mm code has also grown support for stack guard pages since this code was originally written, so the most heinous case of the stack expanding into other mappings is now handled for us. Finally although some other arches have special logic in this path, from what I can tell none of x86, arm64, arm and s390 impose any extra checks other than those in expand_stack(). So drop our complicated logic and like other architectures just let the stack expand as long as its within the rlimit. Signed-off-by: Michael Ellerman <mpe@ellerman.id.au> Tested-by: Daniel Axtens <dja@axtens.net> Link: https://lore.kernel.org/r/20200724092528.1578671-4-mpe@ellerman.id.au |
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| .. | ||
| book3s32 | ||
| book3s64 | ||
| kasan | ||
| nohash | ||
| ptdump | ||
| copro_fault.c | ||
| dma-noncoherent.c | ||
| drmem.c | ||
| fault.c | ||
| highmem.c | ||
| hugetlbpage.c | ||
| init_32.c | ||
| init_64.c | ||
| init-common.c | ||
| ioremap_32.c | ||
| ioremap_64.c | ||
| ioremap.c | ||
| Makefile | ||
| mem.c | ||
| mmap.c | ||
| mmu_context.c | ||
| mmu_decl.h | ||
| numa.c | ||
| pgtable_32.c | ||
| pgtable_64.c | ||
| pgtable-frag.c | ||
| pgtable.c | ||
| slice.c | ||