[PATCH 1/2] arm64: lds: move special code sections out of kernel exec segment

[Ard Biesheuvel]

On Wed, 4 May 2022 at 20:59, Catalin Marinas <catalin.marinas at arm.com> wrote:
>
> On Fri, Apr 29, 2022 at 03:13:46PM +0200, Ard Biesheuvel wrote:
> > There are a few code sections that are emitted into the kernel's
> > executable .text segment simply because they contain code, but are
> > actually never executed via this mapping, so they can happily live in a
> > region that gets mapped without executable permissions, reducing the
> > risk of being gadgetized.
> >
> > Note that the kexec and hibernate region contents are always copied into
> > a fresh page, and so there is no need to align them as long as the
> > overall size of each is below 4 KiB.
> >
> > Signed-off-by: Ard Biesheuvel <ardb at kernel.org>
>
> This patch doesn't get very far. Under qemu, defconfig:
>

Apologies, this is a local rebase error on my part. The .rodata.text
section needs the below added or the following sections will appear
misaligned in memory.

diff --git a/arch/arm64/kernel/vmlinux.lds.S b/arch/arm64/kernel/vmlinux.lds.S
index c33467c6a969..4cea87393c68 100644
--- a/arch/arm64/kernel/vmlinux.lds.S
+++ b/arch/arm64/kernel/vmlinux.lds.S
@@ -212,6 +212,7 @@ SECTIONS
                TRAMP_TEXT
                HIBERNATE_TEXT
                KEXEC_TEXT
+               . = ALIGN(PAGE_SIZE);
        }

        idmap_pg_dir = .;




> EFI stub: Booting Linux Kernel...
> EFI stub: Generating empty DTB
> EFI stub: Exiting boot services...
> [    0.000000] Booting Linux on physical CPU 0x0000000000 [0x000f0510]
> [    0.000000] Linux version 5.18.0-rc3-00008-gfd536ceae063 (cmarinas at gaia) (aarch64-linux-gcc (GCC) 11.1.0, ...)
> [    0.000000] earlycon: pl11 at MMIO 0x0000000009000000 (options '')
> [    0.000000] printk: bootconsole [pl11] enabled
> [    0.000000] efi: EFI v2.70 by EDK II
> [    0.000000] efi: SMBIOS 3.0=0xbbed0000 MEMATTR=0xba919018 ACPI 2.0=0xb61a0018 RNG=0xbbfdbd18 MEMRESERVE=0xb6235f18
> [    0.000000] efi: seeding entropy pool
> [    0.000000] Unable to handle kernel paging request at virtual address fffffbfffda351b4
> [    0.000000] Mem abort info:
> [    0.000000]   ESR = 0x96000007
> [    0.000000]   EC = 0x25: DABT (current EL), IL = 32 bits
> [    0.000000]   SET = 0, FnV = 0
> [    0.000000]   EA = 0, S1PTW = 0
> [    0.000000]   FSC = 0x07: level 3 translation fault
> [    0.000000] Data abort info:
> [    0.000000]   ISV = 0, ISS = 0x00000007
> [    0.000000]   CM = 0, WnR = 0
> [    0.000000] swapper pgtable: 4k pages, 48-bit VAs, pgdp=00000000bf11d000
> [    0.000000] [fffffbfffda351b4] pgd=00000000bf09c003, p4d=00000000bf09c003
> [    0.000000] Unable to handle kernel paging request at virtual address ffff00007f09cff8
> [    0.000000] Mem abort info:
> [    0.000000]   ESR = 0x96000004
> [    0.000000]   EC = 0x25: DABT (current EL), IL = 32 bits
> [    0.000000]   SET = 0, FnV = 0
> [    0.000000]   EA = 0, S1PTW = 0
> [    0.000000]   FSC = 0x04: level 0 translation fault
> [    0.000000] Data abort info:
> [    0.000000]   ISV = 0, ISS = 0x00000004
> [    0.000000]   CM = 0, WnR = 0
> [    0.000000] swapper pgtable: 4k pages, 48-bit VAs, pgdp=00000000bf11d000
> [    0.000000] [ffff00007f09cff8] pgd=0000000000000000, p4d=0000000000000000
> [    0.000000] Internal error: Oops: 96000004 [#1] PREEMPT SMP
> [    0.000000] Modules linked in:
> [    0.000000] CPU: 0 PID: 0 Comm: swapper Not tainted 5.18.0-rc3-00008-gfd536ceae063 #4
> [    0.000000] pstate: 620000c5 (nZCv daIF -PAN -UAO +TCO -DIT -SSBS BTYPE=--)
> [    0.000000] pc : die_kernel_fault+0x2dc/0x394
> [    0.000000] lr : die_kernel_fault+0x2ac/0x394
> [    0.000000] sp : ffffb594f7963ab0
> [    0.000000] x29: ffffb594f7963ab0 x28: ffffb594f7973340 x27: ffffb594f5a20000
> [    0.000000] x26: ffffb594f72c0000 x25: ffffb594f7214000 x24: ffffb594f7d1d000
> [    0.000000] x23: 0000000000000ff8 x22: ffffb594f7963bc0 x21: ffff00007f09c000
> [    0.000000] x20: 0000000096000007 x19: fffffbfffda351b4 x18: ffffffffffffffff
> [    0.000000] x17: 6266666666662073 x16: 736572646461206c x15: ffffb594f7caeb38
> [    0.000000] x14: 0000000000000010 x13: ffffb594f79824a0 x12: 0000000000000036
> [    0.000000] x11: 0000000000000012 x10: ffffb594f79da650 x9 : ffffb594f79824a0
> [    0.000000] x8 : 00000000ffffefff x7 : ffffb594f79da4a0 x6 : 00000000000001b0
> [    0.000000] x5 : 000000000000bff4 x4 : 00000000fffff012 x3 : 0000000000000000
> [    0.000000] x2 : 0000000000000000 x1 : 0000000040000000 x0 : ffffb594f7083618
> [    0.000000] Call trace:
> [    0.000000]  die_kernel_fault+0x2dc/0x394
> [    0.000000]  __do_kernel_fault+0xfc/0x180
> [    0.000000]  do_translation_fault+0x58/0xc0
> [    0.000000]  do_mem_abort+0x44/0x94
> [    0.000000]  el1_abort+0x40/0x6c
> [    0.000000]  el1h_64_sync_handler+0xa4/0xd0
> [    0.000000]  el1h_64_sync+0x64/0x68
> [    0.000000]  paging_init+0x1e4/0x550
> [    0.000000]  setup_arch+0x274/0x608
> [    0.000000]  start_kernel+0x84/0x668
> [    0.000000]  __primary_switched+0xc0/0xc8
> [    0.000000] Code: d0003580 91186000 cb0102b5 b2503eb5 (f8776ab8)
> [    0.000000] ---[ end trace 0000000000000000 ]---
> [    0.000000] Kernel panic - not syncing: Attempted to kill the idle task!
> [    0.000000] ---[ end Kernel panic - not syncing: Attempted to kill the idle task! ]---