Messages in this thread | ![/](/images/icornerl.gif) | | Date | Wed, 03 Apr 2024 19:20:31 +0300 | Subject | Re: [PATCH v2 1/4] arm64: patching: always use fixmap | From | "Jarkko Sakkinen" <> |
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On Wed Apr 3, 2024 at 6:01 PM EEST, Mark Rutland wrote: > For historical reasons, patch_map() won't bother to fixmap non-image > addresses when CONFIG_STRICT_MODULE_RWX=n, matching the behaviour prior > to the introduction of CONFIG_STRICT_MODULE_RWX. However, as arm64 > doesn't select CONFIG_ARCH_OPTIONAL_KERNEL_RWX, CONFIG_MODULES implies > CONFIG_STRICT_MODULE_RWX, so any kernel built with module support will > use the fixmap for any non-image address.
Not familiar with the config flag but I'd guess it is essentially w^x enforcement right for the sections?
> Historically we only used patch_map() for the kernel image and modules, > but these days its also used by BPF and KPROBES to write to read-only > pages of executable text. Currently these both depend on CONFIG_MODULES, > but we'd like to change that in subsequent patches, which will require > using the fixmap regardless of CONFIG_STRICT_MODULE_RWX. > > This patch changes patch_map() to always use the fixmap, and simplifies > the logic: > > * Use is_image_text() directly in the if-else, rather than using a > temporary boolean variable. > > * Use offset_in_page() to get the offset within the mapping. > > * Remove uintaddr and cast the address directly when using > is_image_text(). > > For kernels built with CONFIG_MODULES=y, there should be no functional > change as a result of this patch. > > For kernels built with CONFIG_MODULES=n, patch_map() will use the fixmap > for non-image addresses, but there are no extant users with non-image > addresses when CONFIG_MODULES=n, and hence there should be no functional > change as a result of this patch alone. > > Signed-off-by: Mark Rutland <mark.rutland@arm.com> > Cc: Catalin Marinas <catalin.marinas@arm.com> > Cc: Will Deacon <will@kernel.org> > --- > arch/arm64/kernel/patching.c | 10 +++------- > 1 file changed, 3 insertions(+), 7 deletions(-) > > Catalin, Will, this is a prerequisite for the final two patches in the > series. Are you happy for this go via the tracing tree? > > Mark. > > diff --git a/arch/arm64/kernel/patching.c b/arch/arm64/kernel/patching.c > index 2555349303684..f0f3a2a82ca5a 100644 > --- a/arch/arm64/kernel/patching.c > +++ b/arch/arm64/kernel/patching.c > @@ -30,20 +30,16 @@ static bool is_image_text(unsigned long addr) > > static void __kprobes *patch_map(void *addr, int fixmap) > { > - unsigned long uintaddr = (uintptr_t) addr; > - bool image = is_image_text(uintaddr); > struct page *page; > > - if (image) > + if (is_image_text((unsigned long)addr)) > page = phys_to_page(__pa_symbol(addr)); > - else if (IS_ENABLED(CONFIG_STRICT_MODULE_RWX)) > - page = vmalloc_to_page(addr); > else > - return addr; > + page = vmalloc_to_page(addr); > > BUG_ON(!page); > return (void *)set_fixmap_offset(fixmap, page_to_phys(page) + > - (uintaddr & ~PAGE_MASK)); > + offset_in_page(addr));
nit: could be a single line but i guess it is up to the taste (and subsystem maintainer). I.e. checkpatch will allow it at least.
I don't mind it too much just mentioning for completeness.
> } > > static void __kprobes patch_unmap(int fixmap)
If my assumption about the config flag holds this makes sense:
Reviewed-by: Jarkko Sakkinen <jarkko@kernel.rg>
BR, Jarkko
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