From: Nadav Amit <namit@vmware.com>
To: Ingo Molnar <mingo@redhat.com>,
"Edgecombe, Rick P" <rick.p.edgecombe@intel.com>
Cc: LKML <linux-kernel@vger.kernel.org>, X86 ML <x86@kernel.org>,
"H. Peter Anvin" <hpa@zytor.com>,
Thomas Gleixner <tglx@linutronix.de>,
Borislav Petkov <bp@alien8.de>,
Dave Hansen <dave.hansen@linux.intel.com>,
Peter Zijlstra <peterz@infradead.org>,
Damian Tometzki <linux_dti@icloud.com>,
linux-integrity <linux-integrity@vger.kernel.org>,
LSM List <linux-security-module@vger.kernel.org>,
Andy Lutomirski <luto@kernel.org>,
Kees Cook <keescook@chromium.org>,
Dave Hansen <dave.hansen@intel.com>,
Masami Hiramatsu <mhiramat@kernel.org>
Subject: Re: [PATCH v6 08/10] x86: avoid W^X being broken during modules loading
Date: Wed, 28 Nov 2018 18:59:30 +0000 [thread overview]
Message-ID: <5E938E6F-6BE6-4F86-AC9E-5C389B492682@vmware.com> (raw)
In-Reply-To: <20181120203545.34928-9-namit@vmware.com>
> On Nov 20, 2018, at 12:35 PM, Nadav Amit <namit@vmware.com> wrote:
>
> When modules and BPF filters are loaded, there is a time window in
> which some memory is both writable and executable. An attacker that has
> already found another vulnerability (e.g., a dangling pointer) might be
> able to exploit this behavior to overwrite kernel code. This patch
> prevents having writable executable PTEs in this stage.
>
> In addition, avoiding having R+X mappings can also slightly simplify the
> patching of modules code on initialization (e.g., by alternatives and
> static-key), as would be done in the next patch.
>
> To avoid having W+X mappings, set them initially as RW (NX) and after
> they are set as RO set them as X as well. Setting them as executable is
> done as a separate step to avoid one core in which the old PTE is cached
> (hence writable), and another which sees the updated PTE (executable),
> which would break the W^X protection.
>
> Cc: Andy Lutomirski <luto@kernel.org>
> Cc: Kees Cook <keescook@chromium.org>
> Cc: Peter Zijlstra <peterz@infradead.org>
> Cc: Dave Hansen <dave.hansen@intel.com>
> Cc: Masami Hiramatsu <mhiramat@kernel.org>
> Suggested-by: Thomas Gleixner <tglx@linutronix.de>
> Suggested-by: Andy Lutomirski <luto@amacapital.net>
> Signed-off-by: Nadav Amit <namit@vmware.com>
> ---
> arch/x86/kernel/alternative.c | 28 +++++++++++++++++++++-------
> arch/x86/kernel/module.c | 2 +-
> include/linux/filter.h | 6 ++++++
> kernel/module.c | 10 ++++++++++
> 4 files changed, 38 insertions(+), 8 deletions(-)
>
> diff --git a/arch/x86/kernel/alternative.c b/arch/x86/kernel/alternative.c
> index 8fc4685f3117..18415e3b6000 100644
> --- a/arch/x86/kernel/alternative.c
> +++ b/arch/x86/kernel/alternative.c
> @@ -667,15 +667,29 @@ void __init alternative_instructions(void)
> * handlers seeing an inconsistent instruction while you patch.
> */
> void *__init_or_module text_poke_early(void *addr, const void *opcode,
> - size_t len)
> + size_t len)
> {
> unsigned long flags;
> - local_irq_save(flags);
> - memcpy(addr, opcode, len);
> - local_irq_restore(flags);
> - sync_core();
> - /* Could also do a CLFLUSH here to speed up CPU recovery; but
> - that causes hangs on some VIA CPUs. */
> +
> + if (static_cpu_has(X86_FEATURE_NX) &&
> + is_module_text_address((unsigned long)addr)) {
> + /*
> + * Modules text is marked initially as non-executable, so the
> + * code cannot be running and speculative code-fetches are
> + * prevented. We can just change the code.
> + */
> + memcpy(addr, opcode, len);
> + } else {
> + local_irq_save(flags);
> + memcpy(addr, opcode, len);
> + local_irq_restore(flags);
> + sync_core();
> +
> + /*
> + * Could also do a CLFLUSH here to speed up CPU recovery; but
> + * that causes hangs on some VIA CPUs.
> + */
> + }
> return addr;
> }
>
> diff --git a/arch/x86/kernel/module.c b/arch/x86/kernel/module.c
> index b052e883dd8c..cfa3106faee4 100644
> --- a/arch/x86/kernel/module.c
> +++ b/arch/x86/kernel/module.c
> @@ -87,7 +87,7 @@ void *module_alloc(unsigned long size)
> p = __vmalloc_node_range(size, MODULE_ALIGN,
> MODULES_VADDR + get_module_load_offset(),
> MODULES_END, GFP_KERNEL,
> - PAGE_KERNEL_EXEC, 0, NUMA_NO_NODE,
> + PAGE_KERNEL, 0, NUMA_NO_NODE,
> __builtin_return_address(0));
> if (p && (kasan_module_alloc(p, size) < 0)) {
> vfree(p);
> diff --git a/include/linux/filter.h b/include/linux/filter.h
> index de629b706d1d..ee9ae03c5f56 100644
> --- a/include/linux/filter.h
> +++ b/include/linux/filter.h
> @@ -704,7 +704,13 @@ static inline void bpf_prog_unlock_ro(struct bpf_prog *fp)
>
> static inline void bpf_jit_binary_lock_ro(struct bpf_binary_header *hdr)
> {
> + /*
> + * Perform mapping changes in two stages to avoid opening a time-window
> + * in which a PTE is cached in any TLB as writable, but marked as
> + * executable in the memory-resident mappings (e.g., page-tables).
> + */
> set_memory_ro((unsigned long)hdr, hdr->pages);
> + set_memory_x((unsigned long)hdr, hdr->pages);
> }
>
> static inline void bpf_jit_binary_unlock_ro(struct bpf_binary_header *hdr)
> diff --git a/kernel/module.c b/kernel/module.c
> index 49a405891587..7cb207249437 100644
> --- a/kernel/module.c
> +++ b/kernel/module.c
> @@ -1946,9 +1946,19 @@ void module_enable_ro(const struct module *mod, bool after_init)
> if (!rodata_enabled)
> return;
>
> + /*
> + * Perform mapping changes in two stages to avoid opening a time-window
> + * in which a PTE is cached in any TLB as writable, but marked as
> + * executable in the memory-resident mappings (e.g., page-tables).
> + */
> frob_text(&mod->core_layout, set_memory_ro);
> + frob_text(&mod->core_layout, set_memory_x);
> +
> frob_rodata(&mod->core_layout, set_memory_ro);
> +
> frob_text(&mod->init_layout, set_memory_ro);
> + frob_text(&mod->init_layout, set_memory_x);
> +
> frob_rodata(&mod->init_layout, set_memory_ro);
>
> if (after_init)
> --
> 2.17.1
Rick pointed out that I screwed up ftrace and kprobes.
For kprobes, I think I need to add set_memory_x() to alloc_insn_page() and
change arch_ftrace_update_trampoline().
For arch_ftrace_update_trampoline(), I think I should remove not use
set_memory_rw() when patching in __probe_kernel_write() should be done
through text_poke().
I’ll give it another look and send another version later.
Regards,
Nadav
next prev parent reply other threads:[~2018-11-28 18:59 UTC|newest]
Thread overview: 16+ messages / expand[flat|nested] mbox.gz Atom feed top
2018-11-20 20:35 [PATCH v6 00/10] x86/alternative: text_poke() fixes Nadav Amit
2018-11-20 20:35 ` [PATCH v6 01/10] Fix "x86/alternatives: Lockdep-enforce text_mutex in text_poke*()" Nadav Amit
2018-11-20 20:35 ` [PATCH v6 02/10] x86/jump_label: Use text_poke_early() during early init Nadav Amit
2018-11-20 20:35 ` [PATCH v6 03/10] x86/mm: temporary mm struct Nadav Amit
2018-11-20 20:35 ` [PATCH v6 04/10] fork: provide a function for copying init_mm Nadav Amit
2018-11-20 20:35 ` [PATCH v6 05/10] x86/alternative: initializing temporary mm for patching Nadav Amit
2018-11-20 20:35 ` [PATCH v6 06/10] x86/alternative: use temporary mm for text poking Nadav Amit
2018-11-20 20:35 ` [PATCH v6 07/10] x86/kgdb: avoid redundant comparison of patched code Nadav Amit
2018-11-20 20:35 ` [PATCH v6 08/10] x86: avoid W^X being broken during modules loading Nadav Amit
2018-11-28 18:59 ` Nadav Amit [this message]
2018-11-30 2:32 ` Masami Hiramatsu
2018-11-20 20:35 ` [PATCH v6 09/10] x86/jump-label: remove support for custom poker Nadav Amit
2018-11-20 20:35 ` [PATCH v6 10/10] x86/alternative: remove the return value of text_poke_*() Nadav Amit
2018-11-26 10:32 ` [PATCH v6 00/10] x86/alternative: text_poke() fixes Peter Zijlstra
2018-11-26 17:46 ` Nadav Amit
2018-11-29 12:58 ` Peter Zijlstra
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