Messages in this thread | | | From | Michael Ellerman <> | Subject | Re: [PATCH v4 14/45] powerpc/32s: Don't warn when mapping RO data ROX. | Date | Mon, 25 May 2020 15:40:06 +1000 |
| |
Christophe Leroy <christophe.leroy@csgroup.eu> writes: > Mapping RO data as ROX is not an issue since that data > cannot be modified to introduce an exploit.
Being pedantic: it is still an issue, in that it means there's more targets for a code-reuse attack.
But given the entire kernel text is also available for code-reuse attacks, the RO data is unlikely to contain any useful sequences that aren't also in the kernel text.
> PPC64 accepts to have RO data mapped ROX, as a trade off > between kernel size and strictness of protection. > > On PPC32, kernel size is even more critical as amount of > memory is usually small.
Yep, I think it's a reasonable trade off to make.
cheers
> Depending on the number of available IBATs, the last IBATs > might overflow the end of text. Only warn if it crosses > the end of RO data. > > Signed-off-by: Christophe Leroy <christophe.leroy@csgroup.eu> > --- > arch/powerpc/mm/book3s32/mmu.c | 6 ++++-- > 1 file changed, 4 insertions(+), 2 deletions(-) > > diff --git a/arch/powerpc/mm/book3s32/mmu.c b/arch/powerpc/mm/book3s32/mmu.c > index 39ba53ca5bb5..a9b2cbc74797 100644 > --- a/arch/powerpc/mm/book3s32/mmu.c > +++ b/arch/powerpc/mm/book3s32/mmu.c > @@ -187,6 +187,7 @@ void mmu_mark_initmem_nx(void) > int i; > unsigned long base = (unsigned long)_stext - PAGE_OFFSET; > unsigned long top = (unsigned long)_etext - PAGE_OFFSET; > + unsigned long border = (unsigned long)__init_begin - PAGE_OFFSET; > unsigned long size; > > if (IS_ENABLED(CONFIG_PPC_BOOK3S_601)) > @@ -201,9 +202,10 @@ void mmu_mark_initmem_nx(void) > size = block_size(base, top); > size = max(size, 128UL << 10); > if ((top - base) > size) { > - if (strict_kernel_rwx_enabled()) > - pr_warn("Kernel _etext not properly aligned\n"); > size <<= 1; > + if (strict_kernel_rwx_enabled() && base + size > border) > + pr_warn("Some RW data is getting mapped X. " > + "Adjust CONFIG_DATA_SHIFT to avoid that.\n"); > } > setibat(i++, PAGE_OFFSET + base, base, size, PAGE_KERNEL_TEXT); > base += size; > -- > 2.25.0
| |