| From | Ard Biesheuvel <> | Subject | [PATCH v3 59/60] mm: add arch hook to validate mmap() prot flags | Date | Tue, 7 Mar 2023 15:05:21 +0100 |
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Add a hook to permit architectures to perform validation on the prot flags passed to mmap(), like arch_validate_prot() does for mprotect(). This will be used by arm64 to reject PROT_WRITE+PROT_EXEC mappings on configurations that run with WXN enabled.
Reviewed-by: Kees Cook <keescook@chromium.org> Signed-off-by: Ard Biesheuvel <ardb@kernel.org> --- include/linux/mman.h | 15 +++++++++++++++ mm/mmap.c | 3 +++ 2 files changed, 18 insertions(+)
diff --git a/include/linux/mman.h b/include/linux/mman.h index cee1e4b566d80095..25ffe6948fa21ff8 100644 --- a/include/linux/mman.h +++ b/include/linux/mman.h @@ -120,6 +120,21 @@ static inline bool arch_validate_flags(unsigned long flags) #define arch_validate_flags arch_validate_flags #endif +#ifndef arch_validate_mmap_prot +/* + * This is called from mmap(), which ignores unknown prot bits so the default + * is to accept anything. + * + * Returns true if the prot flags are valid + */ +static inline bool arch_validate_mmap_prot(unsigned long prot, + unsigned long addr) +{ + return true; +} +#define arch_validate_mmap_prot arch_validate_mmap_prot +#endif + /* * Optimisation macro. It is equivalent to: * (x & bit1) ? bit2 : 0 diff --git a/mm/mmap.c b/mm/mmap.c index 740b54be3ed4140f..02ccd45df0194796 100644 --- a/mm/mmap.c +++ b/mm/mmap.c @@ -1214,6 +1214,9 @@ unsigned long do_mmap(struct file *file, unsigned long addr, if (!(file && path_noexec(&file->f_path))) prot |= PROT_EXEC; + if (!arch_validate_mmap_prot(prot, addr)) + return -EACCES; + /* force arch specific MAP_FIXED handling in get_unmapped_area */ if (flags & MAP_FIXED_NOREPLACE) flags |= MAP_FIXED; -- 2.39.2
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