On Fri, May 12, 2023 at 02:41:50PM -0400, Kent Overstreet wrote: > On Thu, May 11, 2023 at 03:28:40PM -0700, Kees Cook wrote: > > On Wed, May 10, 2023 at 03:05:48PM +0000, Johannes Thumshirn wrote: > > > On 09.05.23 18:56, Kent Overstreet wrote: > > > > +/** > > > > + * vmalloc_exec - allocate virtually contiguous, executable memory > > > > + * @size: allocation size > > > > + * > > > > + * Kernel-internal function to allocate enough pages to cover @size > > > > + * the page level allocator and map them into contiguous and > > > > + * executable kernel virtual space. > > > > + * > > > > + * For tight control over page level allocator and protection flags > > > > + * use __vmalloc() instead. > > > > + * > > > > + * Return: pointer to the allocated memory or %NULL on error > > > > + */ > > > > +void *vmalloc_exec(unsigned long size, gfp_t gfp_mask) > > > > +{ > > > > + return __vmalloc_node_range(size, 1, VMALLOC_START, VMALLOC_END, > > > > + gfp_mask, PAGE_KERNEL_EXEC, VM_FLUSH_RESET_PERMS, > > > > + NUMA_NO_NODE, __builtin_return_address(0)); > > > > +} > > > > +EXPORT_SYMBOL_GPL(vmalloc_exec); > > > > > > Uh W+X memory reagions. > > > The 90s called, they want their shellcode back. > > > > Just to clarify: the kernel must never create W+X memory regions. So, > > no, do not reintroduce vmalloc_exec(). > > > > Dynamic code areas need to be constructed in a non-executable memory, > > then switched to read-only and verified to still be what was expected, > > and only then made executable. > > So if we're opening this up to the topic if what an acceptible API would > look like - how hard is this requirement? > > The reason is that the functions we're constructing are only ~50 bytes, > so we don't want to be burning a full page per function (particularly > for the 64kb page architectures...) For something that small, why not use the text_poke API? -- Kees Cook