d835f9c4ed
[ Upstream commit 111bcb37385353f0510e5847d5abcd1c613dba23 ] 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") Reported-by: Sachin Sant <sachinp@linux.ibm.com> Tested-by: Sachin Sant <sachinp@linux.ibm.com> Signed-off-by: Michael Ellerman <mpe@ellerman.id.au> Link: https://lore.kernel.org/r/20230110124753.1325426-2-mpe@ellerman.id.au Signed-off-by: Sasha Levin <sashal@kernel.org>
Linux kernel
============
There are several guides for kernel developers and users. These guides can
be rendered in a number of formats, like HTML and PDF. Please read
Documentation/admin-guide/README.rst first.
In order to build the documentation, use ``make htmldocs`` or
``make pdfdocs``. The formatted documentation can also be read online at:
https://www.kernel.org/doc/html/latest/
There are various text files in the Documentation/ subdirectory,
several of them using the Restructured Text markup notation.
Please read the Documentation/process/changes.rst file, as it contains the
requirements for building and running the kernel, and information about
the problems which may result by upgrading your kernel.