From: Joerg Roedel jroedel@suse.de
commit de2b41be8fcccb2f5b6c480d35df590476344201 upstream.
On x86-32 the idt_table with 256 entries needs only 2048 bytes. It is page-aligned, but the end of the .bss..page_aligned section is not guaranteed to be page-aligned.
As a result, objects from other .bss sections may end up on the same 4k page as the idt_table, and will accidentially get mapped read-only during boot, causing unexpected page-faults when the kernel writes to them.
This could be worked around by making the objects in the page aligned sections page sized, but that's wrong.
Explicit sections which store only page aligned objects have an implicit guarantee that the object is alone in the page in which it is placed. That works for all objects except the last one. That's inconsistent.
Enforcing page sized objects for these sections would wreckage memory sanitizers, because the object becomes artificially larger than it should be and out of bound access becomes legit.
Align the end of the .bss..page_aligned and .data..page_aligned section on page-size so all objects places in these sections are guaranteed to have their own page.
[ tglx: Amended changelog ]
Signed-off-by: Joerg Roedel jroedel@suse.de Signed-off-by: Thomas Gleixner tglx@linutronix.de Reviewed-by: Kees Cook keescook@chromium.org Cc: stable@vger.kernel.org Link: https://lkml.kernel.org/r/20200721093448.10417-1-joro@8bytes.org Signed-off-by: Greg Kroah-Hartman gregkh@linuxfoundation.org
--- arch/x86/kernel/vmlinux.lds.S | 1 + include/asm-generic/vmlinux.lds.h | 5 ++++- 2 files changed, 5 insertions(+), 1 deletion(-)
--- a/arch/x86/kernel/vmlinux.lds.S +++ b/arch/x86/kernel/vmlinux.lds.S @@ -362,6 +362,7 @@ SECTIONS .bss : AT(ADDR(.bss) - LOAD_OFFSET) { __bss_start = .; *(.bss..page_aligned) + . = ALIGN(PAGE_SIZE); *(BSS_MAIN) BSS_DECRYPTED . = ALIGN(PAGE_SIZE); --- a/include/asm-generic/vmlinux.lds.h +++ b/include/asm-generic/vmlinux.lds.h @@ -306,7 +306,8 @@
#define PAGE_ALIGNED_DATA(page_align) \ . = ALIGN(page_align); \ - *(.data..page_aligned) + *(.data..page_aligned) \ + . = ALIGN(page_align);
#define READ_MOSTLY_DATA(align) \ . = ALIGN(align); \ @@ -695,7 +696,9 @@ . = ALIGN(bss_align); \ .bss : AT(ADDR(.bss) - LOAD_OFFSET) { \ BSS_FIRST_SECTIONS \ + . = ALIGN(PAGE_SIZE); \ *(.bss..page_aligned) \ + . = ALIGN(PAGE_SIZE); \ *(.dynbss) \ *(BSS_MAIN) \ *(COMMON) \