Re: [PATCH 1/4] mm/vmalloc: allow arch-specific vmalloc_node overrides

Christophe Leroy
2024-02-21T06:59:06Z

Le 20/02/2024 à 21:32, Maxwell Bland a écrit :
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>
> 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.
>
> 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.
>
> Two benefits of this approach are (1) greater flexibility to each
> architecture for handling of virtual memory while not compromising the
> kernel's vmalloc logic and (2) more uniform use of the __vmalloc_node
> interface, reserving the more specialized __vmalloc_node_range for more
> specialized cases, such as kasan's shadow memory.

I'm not sure I understand the message. What I understand is that you
allow architectures to override vmalloc_node().

In the code you add __weak for that. But you also add the flags to the
parameters and I can't understand why when reading the above description.

Christophe