> On 10-Jan-2023, at 6:17 PM, Michael Ellerman <m...@ellerman.id.au> wrote:
>
> If a relocatable kernel is loaded at a non-zero address and told not to
> relocate to zero (kdump or RELOCATABLE_TEST), the mapping of the
> interrupt code at zero is left with RWX permissions.
>
> That is a security weakness, and leads to a warning at boot if
> CONFIG_DEBUG_WX is enabled:
>
> powerpc/mm: Found insecure W+X mapping at address
> 00000000056435bc/0xc000000000000000
> WARNING: CPU: 1 PID: 1 at arch/powerpc/mm/ptdump/ptdump.c:193
> note_page+0x484/0x4c0
> CPU: 1 PID: 1 Comm: swapper/0 Not tainted
> 6.2.0-rc1-00001-g8ae8e98aea82-dirty #175
> Hardware name: IBM pSeries (emulated by qemu) POWER9 (raw) 0x4e1202
> 0xf000005 of:SLOF,git-dd0dca hv:linux,kvm pSeries
> NIP: c0000000004a1c34 LR: c0000000004a1c30 CTR: 0000000000000000
> REGS: c000000003503770 TRAP: 0700 Not tainted
> (6.2.0-rc1-00001-g8ae8e98aea82-dirty)
> MSR: 8000000002029033 <SF,VEC,EE,ME,IR,DR,RI,LE> CR: 24000220 XER:
> 00000000
> CFAR: c000000000545a58 IRQMASK: 0
> ...
> NIP note_page+0x484/0x4c0
> LR note_page+0x480/0x4c0
> Call Trace:
> note_page+0x480/0x4c0 (unreliable)
> ptdump_pmd_entry+0xc8/0x100
> walk_pgd_range+0x618/0xab0
> walk_page_range_novma+0x74/0xc0
> ptdump_walk_pgd+0x98/0x170
> ptdump_check_wx+0x94/0x100
> mark_rodata_ro+0x30/0x70
> kernel_init+0x78/0x1a0
> ret_from_kernel_thread+0x5c/0x64
>
> The fix has two parts. Firstly the pages from zero up to the end of
> interrupts need to be marked read-only, so that they are left with R-X
> permissions. Secondly the mapping logic needs to be taught to ensure
> there is a page boundary at the end of the interrupt region, so that the
> permission change only applies to the interrupt text, and not the region
> following it.
>
> Fixes: c55d7b5e6426 ("powerpc: Remove STRICT_KERNEL_RWX incompatibility with
> RELOCATABLE")
> Signed-off-by: Michael Ellerman <m...@ellerman.id.au>
> ---
Thanks Michael. This fixes the problem reported earlier
https://lore.kernel.org/linuxppc-dev/48206911-fd3d-401a-a69d-1a79403e7...@linux.ibm.com/
Reported-by: Sachin Sant <sach...@linux.ibm.com>
Tested-by: Sachin Sant <sach...@linux.ibm.com>
- Sachin
