Resending v2 for review comments. This patch series addresses following to improve kfence support on Powerpc. 1. Usage of copy_from_kernel_nofault() within kernel, such as read from /proc/kcore can cause kfence to report false negatives. This is similar to what was reported on s390. [1] [1]: https://lore.kernel.org/all/20230213183858.1473681-1-hca@xxxxxxxxxxxxx/ Hence this series adds patch-1 as a kfence kunit test to detect copy_from_kernel_nofault() case. I assume the same might be needed for all other archs as well (Please correct if this understanding is wrong). Patch-2, thus adds a fix to handle this case in ___do_page_fault() for powerpc. 2. (book3s64) Kfence depends upon debug_pagealloc infrastructure on Hash. debug_pagealloc allocates a linear map based on the size of the DRAM i.e. 1 byte for every 64k page. That means for a 16TB DRAM, it will need 256MB memory for linear map. Memory for linear map on pseries comes from RMA region which has size limitation. On P8 RMA is 512MB, in which we also fit crash kernel at 256MB, paca allocations and emergency stacks. That means there is not enough memory in the RMA region for the linear map based on DRAM size (required by debug_pagealloc). Now kfence only requires memory for it's kfence objects. kfence by default requires only (255 + 1) * 2 i.e. 32 MB for 64k pagesize. Summary of patches ================== This series in Patch-1 adds a kfence kunit testcase to detect copy_from_kernel_nofault() case. I assume the same should be needed for all other archs as well. Patch-2 adds a fix to handle this false negatives from copy_from_kernel_nofault(). Patch[3-9] removes the direct dependency of kfence on debug_pagealloc infrastructure. We make Hash kernel linear map functions to take linear map array as a parameter so that it can support debug_pagealloc and kfence individually. That means we don't need to keep the size of the linear map to be DRAM_SIZE >> PAGE_SHIFT anymore for kfence. Patch-10: Adds kfence support with above (abstracted out) kernel linear map infrastructure. With it, this also fixes, the boot failure problem when kfence gets enabled on Hash with >=16TB of RAM. Patch-11 & Patch-12: Ensure late initialization of kfence is disabled for both Hash and Radix due to linear mapping size limiations. Commit gives more description. Patch-13: Early detects if debug_pagealloc cannot be enabled (due to RMA size limitation) so that the linear mapping size can be set correctly during init. Testing: ======== It passes kfence kunit tests with Hash and Radix. [ 44.355173][ T1] # kfence: pass:27 fail:0 skip:0 total:27 [ 44.358631][ T1] # Totals: pass:27 fail:0 skip:0 total:27 [ 44.365570][ T1] ok 1 kfence Future TODO: ============ When kfence on Hash gets enabled, the kernel linear map uses PAGE_SIZE mapping rather than 16MB mapping. This should be improved in future. v1 -> v2: ========= 1. Added a kunit testcase patch-1. 2. Fixed a false negative with copy_from_kernel_nofault() in patch-2. 3. Addressed review comments from Christophe Leroy. 4. Added patch-13. Nirjhar Roy (1): mm/kfence: Add a new kunit test test_use_after_free_read_nofault() Ritesh Harjani (IBM) (12): powerpc: mm: Fix kfence page fault reporting book3s64/hash: Remove kfence support temporarily book3s64/hash: Refactor kernel linear map related calls book3s64/hash: Add hash_debug_pagealloc_add_slot() function book3s64/hash: Add hash_debug_pagealloc_alloc_slots() function book3s64/hash: Refactor hash__kernel_map_pages() function book3s64/hash: Make kernel_map_linear_page() generic book3s64/hash: Disable debug_pagealloc if it requires more memory book3s64/hash: Add kfence functionality book3s64/radix: Refactoring common kfence related functions book3s64/hash: Disable kfence if not early init book3s64/hash: Early detect debug_pagealloc size requirement arch/powerpc/include/asm/kfence.h | 8 +- arch/powerpc/mm/book3s64/hash_utils.c | 364 +++++++++++++++++------ arch/powerpc/mm/book3s64/pgtable.c | 13 + arch/powerpc/mm/book3s64/radix_pgtable.c | 12 - arch/powerpc/mm/fault.c | 10 +- arch/powerpc/mm/init-common.c | 1 + mm/kfence/kfence_test.c | 17 ++ 7 files changed, 318 insertions(+), 107 deletions(-) -- 2.46.0
