Le 21/02/2024 à 06:43, Christoph Hellwig a écrit :

On Tue, Feb 20, 2024 at 02:32:53PM -0600, Maxwell Bland wrote:

quoted

Present non-uniform use of __vmalloc_node and __vmalloc_node_range makes
enforcing appropriate code and data seperation untenable on certain
microarchitectures, as VMALLOC_START and VMALLOC_END are monolithic
while the use of the vmalloc interface is non-monolithic: in particular,
appropriate randomness in ASLR makes it such that code regions must fall
in some region between VMALLOC_START and VMALLOC_end, but this
necessitates that code pages are intermingled with data pages, meaning
code-specific protections, such as arm64's PXNTable, cannot be
performantly runtime enforced.

That's not actually true.  We have MODULE_START/END to separate them,
which is used by mips only for now.

We have MODULES_VADDR and MODULES_END that are used by arm, arm64, 
loongarcg, powerpc, riscv, s390, sparc, x86_64

is_vmalloc_or_module_addr() is using MODULES_VADDR so I guess this 
function fails on mips ?

quoted

The solution to this problem allows architectures to override the
vmalloc wrapper functions by enforcing that the rest of the kernel does
not reimplement __vmalloc_node by using __vmalloc_node_range with the
same parameters as __vmalloc_node or provides a __weak tag to those
functions using __vmalloc_node_range with parameters repeating those of
__vmalloc_node.

I'm really not too happy about overriding the functions.  Especially
as the separation is a generally good idea and it would be good to
move everyone (or at least all modern architectures) over to a scheme
like this.