[PATCH v3 0/5] hardening : prevent write to proces's read-only pages

Lev Olshvang
2020-04-16T15:59:43Z

v3 --> v4
patch of v3 was mailformed . Sendimg again
I removed architectures I can not test patch (PPC, unicore, um)
I tested it only on arm and x86, x86_64
v2 --> v3
Split patch to architecture independ part and separate patches
for architectures that have arch_vma_access_permitted() handler.
I tested it only on arm and x86
v1 --> v2
I sent empty v1 patch, just resending
v0 --> v1
---
Added sysctl_forbid_write_ro_mem to control whether to allow write
or deny. (Advised by Kees Cook, KSPP issue 37)
It has values range [0-2] and it gets the initial value from
CONFIG_PROTECT_READONLY_USER_MEMORY (defaulted to 0, so it cant break)
Setting it to 0 disables write checks.
Setting it to 1 deny writes from other processes.
Setting it to 2 deny writes from any processes including itself
----
v0
----

The purpose of this patch is produce hardened kernel for Embedded
or Production systems.
This patch shouild close issue 37 opened by Kees Cook in KSPP project

Typically debuggers, such as gdb, write to read-only code [text]
sections of target process.(ptrace)
This kind of page protectiion violation raises minor page fault, but
kernel's fault handler allows it by default.
This is clearly attack surface for adversary.

The proposed kernel hardening configuration option checks the type of
protection of the foreign vma and blocks writes to read only vma.

When enabled, it will stop attacks modifying code or jump tables, etc.

Code of arch_vma_access_permitted() function was extended to
check foreign vma flags.

Tested on x86_64 and ARM(QEMU) with dd command which writes to
/proc/PID/mem in r--p or r--xp of vma area addresses range

dd reports IO failure when tries to write to adress taken from
from /proc/PID/maps (PLT or code section)

Lev Olshvang (5):
Hardening x86: Forbid writes to read-only memory pages of a process
Hardening PowerPC: Forbid writes to read-only memory pages of a
process
Hardening um: Forbid writes to read-only memory pages of a process
Hardening unicore32: Forbid writes to read-only memory pages of a
process
Hardening : PPC book3s64: Forbid writes to read-only memory pages of a
process

arch/powerpc/include/asm/mmu_context.h | 9 +--------
arch/powerpc/mm/book3s64/pkeys.c | 5 -----
arch/um/include/asm/mmu_context.h | 8 +-------
arch/unicore32/include/asm/mmu_context.h | 7 +------
arch/x86/include/asm/mmu_context.h | 8 +-------
5 files changed, 4 insertions(+), 33 deletions(-)

--
2.17.1