On Mon, Aug 14, 2023 at 09:54:24AM +0800, Lianbo Jiang wrote:
> Currently, crash-utility still depends on detecting the kernel version,
> or the asm instruction 'bswap' on X86 64/X86 architectures to decide how
> to deal with the freelist ptr obfuscation, when kernel option
> CONFIG_SLAB_FREELIST_HARDENED is enabled.
>
> As you known, the bit diffusion for freelist ptr obfuscation has
> experienced the changes several times on the kernel side, For most
> distributions, usually they might backport these kernel patches from
> upstream, especially for the old kernel, the 'kmem -s|-S' will fail with
> an error "invalid freepointer", which can be observed on ppc64le and
> S390x architectures, etc. That is really not friendly.
>
> Given that, let's fix the above issues this time, and it won't rely
> on the linux version number or asm instruction 'bswap' to decide how to
> dereference the freelist ptr.
>
> Reported-by: Lucas Oakley <soakley@xxxxxxxxxx>
> Signed-off-by: Lianbo Jiang <lijiang@xxxxxxxxxx>
> ---
> memory.c | 9 ++++++---
> 1 file changed, 6 insertions(+), 3 deletions(-)
>
> diff --git a/memory.c b/memory.c
> index 626c6039c6d9..562914ee9230 100644
> --- a/memory.c
> +++ b/memory.c
> @@ -19654,9 +19654,12 @@ freelist_ptr(struct meminfo *si, ulong ptr, ulong ptr_addr)
> if (VALID_MEMBER(kmem_cache_random)) {
> /* CONFIG_SLAB_FREELIST_HARDENED */
>
> - if (THIS_KERNEL_VERSION >= LINUX(5,7,0))
> - ptr_addr = (sizeof(long) == 8) ? bswap_64(ptr_addr)
> - : bswap_32(ptr_addr);
> + ulong addr = (sizeof(long) == 8) ? bswap_64(ptr_addr) : bswap_32(ptr_addr);
> + addr = ptr ^ si->random ^ addr;
> +
> + if (!addr || accessible(addr))
> + return addr;
> +
> return (ptr ^ si->random ^ ptr_addr);
> } else
> return ptr;
> --
> 2.37.1
>
Lucas and I finished testing this set across x86_64, AARCH64, PPC64LE and
S390X with no hiccups observed.
Thanks for following it up!
Acked-by: Rafael Aquini <aquini@xxxxxxxxxx>
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