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When STRICT_KERNEL_RWX is set, any change of permissions on any kernel mapping (vmalloc/modules/kernel text...etc) should be applied on its linear mapping alias. The problem is that the riscv kernel uses huge mappings for the linear mapping and walk_page_range_novma() does not split those huge mappings. So this patchset implements such split in order to apply fine-grained permissions on the linear mapping. Below is the difference before and after (the first PUD mapping is split into PTE/PMD mappings): Before: ---[ Linear mapping ]--- 0xffffaf8000080000-0xffffaf8000200000 0x0000000080080000 1536K PTE D A G . . W R V 0xffffaf8000200000-0xffffaf8077c00000 0x0000000080200000 1914M PMD D A G . . W R V 0xffffaf8077c00000-0xffffaf8078800000 0x00000000f7c00000 12M PMD D A G . . . R V 0xffffaf8078800000-0xffffaf8078c00000 0x00000000f8800000 4M PMD D A G . . W R V 0xffffaf8078c00000-0xffffaf8079200000 0x00000000f8c00000 6M PMD D A G . . . R V 0xffffaf8079200000-0xffffaf807e600000 0x00000000f9200000 84M PMD D A G . . W R V 0xffffaf807e600000-0xffffaf807e716000 0x00000000fe600000 1112K PTE D A G . . W R V 0xffffaf807e717000-0xffffaf807e71a000 0x00000000fe717000 12K PTE D A G . . W R V 0xffffaf807e71d000-0xffffaf807e71e000 0x00000000fe71d000 4K PTE D A G . . W R V 0xffffaf807e722000-0xffffaf807e800000 0x00000000fe722000 888K PTE D A G . . W R V 0xffffaf807e800000-0xffffaf807fe00000 0x00000000fe800000 22M PMD D A G . . W R V 0xffffaf807fe00000-0xffffaf807ff54000 0x00000000ffe00000 1360K PTE D A G . . W R V 0xffffaf807ff55000-0xffffaf8080000000 0x00000000fff55000 684K PTE D A G . . W R V 0xffffaf8080000000-0xffffaf8400000000 0x0000000100000000 14G PUD D A G . . W R V After: ---[ Linear mapping ]--- 0xffffaf8000080000-0xffffaf8000200000 0x0000000080080000 1536K PTE D A G . . W R V 0xffffaf8000200000-0xffffaf8077c00000 0x0000000080200000 1914M PMD D A G . . W R V 0xffffaf8077c00000-0xffffaf8078800000 0x00000000f7c00000 12M PMD D A G . . . R V 0xffffaf8078800000-0xffffaf8078a00000 0x00000000f8800000 2M PMD D A G . . W R V 0xffffaf8078a00000-0xffffaf8078c00000 0x00000000f8a00000 2M PTE D A G . . W R V 0xffffaf8078c00000-0xffffaf8079200000 0x00000000f8c00000 6M PMD D A G . . . R V 0xffffaf8079200000-0xffffaf807e600000 0x00000000f9200000 84M PMD D A G . . W R V 0xffffaf807e600000-0xffffaf807e716000 0x00000000fe600000 1112K PTE D A G . . W R V 0xffffaf807e717000-0xffffaf807e71a000 0x00000000fe717000 12K PTE D A G . . W R V 0xffffaf807e71d000-0xffffaf807e71e000 0x00000000fe71d000 4K PTE D A G . . W R V 0xffffaf807e722000-0xffffaf807e800000 0x00000000fe722000 888K PTE D A G . . W R V 0xffffaf807e800000-0xffffaf807fe00000 0x00000000fe800000 22M PMD D A G . . W R V 0xffffaf807fe00000-0xffffaf807ff54000 0x00000000ffe00000 1360K PTE D A G . . W R V 0xffffaf807ff55000-0xffffaf8080000000 0x00000000fff55000 684K PTE D A G . . W R V 0xffffaf8080000000-0xffffaf8080800000 0x0000000100000000 8M PMD D A G . . W R V 0xffffaf8080800000-0xffffaf8080af6000 0x0000000100800000 3032K PTE D A G . . W R V 0xffffaf8080af6000-0xffffaf8080af8000 0x0000000100af6000 8K PTE D A G . X . R V 0xffffaf8080af8000-0xffffaf8080c00000 0x0000000100af8000 1056K PTE D A G . . W R V 0xffffaf8080c00000-0xffffaf8081a00000 0x0000000100c00000 14M PMD D A G . . W R V 0xffffaf8081a00000-0xffffaf8081a40000 0x0000000101a00000 256K PTE D A G . . W R V 0xffffaf8081a40000-0xffffaf8081a44000 0x0000000101a40000 16K PTE D A G . X . R V 0xffffaf8081a44000-0xffffaf8081a52000 0x0000000101a44000 56K PTE D A G . . W R V 0xffffaf8081a52000-0xffffaf8081a54000 0x0000000101a52000 8K PTE D A G . X . R V ... 0xffffaf809e800000-0xffffaf80c0000000 0x000000011e800000 536M PMD D A G . . W R V 0xffffaf80c0000000-0xffffaf8400000000 0x0000000140000000 13G PUD D A G . . W R V Note that this also fixes memfd_secret() syscall which uses set_direct_map_invalid_noflush() and set_direct_map_default_noflush() to remove the pages from the linear mapping. Below is the kernel page table while a memfd_secret() syscall is running, you can see all the !valid page table entries in the linear mapping: ... 0xffffaf8082240000-0xffffaf8082241000 0x0000000102240000 4K PTE D A G . . W R . 0xffffaf8082241000-0xffffaf8082250000 0x0000000102241000 60K PTE D A G . . W R V 0xffffaf8082250000-0xffffaf8082252000 0x0000000102250000 8K PTE D A G . . W R . 0xffffaf8082252000-0xffffaf8082256000 0x0000000102252000 16K PTE D A G . . W R V 0xffffaf8082256000-0xffffaf8082257000 0x0000000102256000 4K PTE D A G . . W R . 0xffffaf8082257000-0xffffaf8082258000 0x0000000102257000 4K PTE D A G . . W R V 0xffffaf8082258000-0xffffaf8082259000 0x0000000102258000 4K PTE D A G . . W R . 0xffffaf8082259000-0xffffaf808225a000 0x0000000102259000 4K PTE D A G . . W R V 0xffffaf808225a000-0xffffaf808225c000 0x000000010225a000 8K PTE D A G . . W R . 0xffffaf808225c000-0xffffaf8082266000 0x000000010225c000 40K PTE D A G . . W R V 0xffffaf8082266000-0xffffaf8082268000 0x0000000102266000 8K PTE D A G . . W R . 0xffffaf8082268000-0xffffaf8082284000 0x0000000102268000 112K PTE D A G . . W R V 0xffffaf8082284000-0xffffaf8082288000 0x0000000102284000 16K PTE D A G . . W R . 0xffffaf8082288000-0xffffaf808229c000 0x0000000102288000 80K PTE D A G . . W R V 0xffffaf808229c000-0xffffaf80822a0000 0x000000010229c000 16K PTE D A G . . W R . 0xffffaf80822a0000-0xffffaf80822a5000 0x00000001022a0000 20K PTE D A G . . W R V 0xffffaf80822a5000-0xffffaf80822a6000 0x00000001022a5000 4K PTE D A G . . . R V 0xffffaf80822a6000-0xffffaf80822ab000 0x00000001022a6000 20K PTE D A G . . W R V ... And when the memfd_secret() fd is released, the linear mapping is correctly reset: ... 0xffffaf8082240000-0xffffaf80822a5000 0x0000000102240000 404K PTE D A G . . W R V 0xffffaf80822a5000-0xffffaf80822a6000 0x00000001022a5000 4K PTE D A G . . . R V 0xffffaf80822a6000-0xffffaf80822af000 0x00000001022a6000 36K PTE D A G . . W R V ... Signed-off-by: Alexandre Ghiti <alexghiti@rivosinc.com> Link: https://lore.kernel.org/r/20231108075930.7157-3-alexghiti@rivosinc.com Signed-off-by: Palmer Dabbelt <palmer@rivosinc.com>
Linux kernel
============
There are several guides for kernel developers and users. These guides can
be rendered in a number of formats, like HTML and PDF. Please read
Documentation/admin-guide/README.rst first.
In order to build the documentation, use ``make htmldocs`` or
``make pdfdocs``. The formatted documentation can also be read online at:
https://www.kernel.org/doc/html/latest/
There are various text files in the Documentation/ subdirectory,
several of them using the Restructured Text markup notation.
Please read the Documentation/process/changes.rst file, as it contains the
requirements for building and running the kernel, and information about
the problems which may result by upgrading your kernel.