linux-hardening - Re: [PATCH v2] x86/mm: Refuse W^X violations

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Date:   Mon, 24 Oct 2022 11:27:30 -0400
From:   Steven Rostedt <rostedt@...dmis.org>
To:     Peter Zijlstra <peterz@...radead.org>
Cc:     Dave Hansen <dave.hansen@...el.com>, x86@...nel.org,
        linux-kernel@...r.kernel.org, linux-hardening@...r.kernel.org,
        keescook@...omium.org, Sean Christopherson <seanjc@...gle.com>,
        Linux Trace Kernel <linux-trace-kernel@...r.kernel.org>
Subject: Re: [PATCH v2] x86/mm: Refuse W^X violations

On Mon, 29 Aug 2022 12:18:03 +0200
Peter Zijlstra <peterz@...radead.org> wrote:

> x86 has STRICT_*_RWX, but not even a warning when someone violates it.
> 
> Add this warning and fully refuse the transition.
> 
> Signed-off-by: Peter Zijlstra (Intel) <peterz@...radead.org>

So, this now triggers on enabling function tracing at boot up:

  "ftrace=function"

This:

SLUB: HWalign=64, Order=0-3, MinObjects=0, CPUs=4, Nodes=1
Kernel/User page tables isolation: enabled
ftrace: allocating 68738 entries in 269 pages
ftrace: allocated 269 pages with 4 groups
Starting tracer 'function'
------------[ cut here ]------------
CPA detected W^X violation: 8000000000000063 -> 0000000000000063 range: 0xffffffffc0013000 - 0xffffffffc0013fff PFN 10031b
WARNING: CPU: 0 PID: 0 at arch/x86/mm/pat/set_memory.c:609 verify_rwx+0x61/0x6d
Modules linked in:
CPU: 0 PID: 0 Comm: swapper Not tainted 6.1.0-rc1-test+ #3
Hardware name: MSI MS-7823/CSM-H87M-G43 (MS-7823), BIOS V1.6 02/22/2014
RIP: 0010:verify_rwx+0x61/0x6d
Code: e5 01 00 75 27 49 c1 e0 0c 48 89 d1 48 89 fe 48 c7 c7 5b b3 92 84 4e 8d 44 02 ff 48 89 da c6 05 71 29 e5 01 01 e8 35 90 e2 00 <0f> 0b 48 89 d8 5b 5d e9 6f 95 1a 01 0f 1f 44 00 00 55 48 89 e5 53
RSP: 0000:ffffffff84c03b08 EFLAGS: 00010086
RAX: 0000000000000000 RBX: 0000000000000063 RCX: 0000000000000003
RDX: 0000000000000003 RSI: ffffffff84c039b0 RDI: 0000000000000001
RBP: ffffffff84c03b10 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000025 R12: ffff8e730031c098
R13: 000000000010031b R14: 800000010031b063 R15: 8000000000000063
FS:  0000000000000000(0000) GS:ffff8e7416a00000(0000) knlGS:0000000000000000
CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: ffff8e73fd801000 CR3: 00000001fcc22001 CR4: 00000000000606f0
Call Trace:
 <TASK>
 __change_page_attr_set_clr+0x146/0x8a6
 ? __mutex_unlock_slowpath+0x41/0x213
 ? mutex_unlock+0x12/0x18
 ? _vm_unmap_aliases+0x126/0x136
 change_page_attr_set_clr+0x135/0x268
 ? find_vmap_area+0x32/0x3e
 ? __fentry__+0x10/0x10
 change_page_attr_clear.constprop.0+0x16/0x1c
 set_memory_x+0x2c/0x32
 arch_ftrace_update_trampoline+0x218/0x2db
 ? ftrace_caller_op_ptr+0x17/0x17
 ftrace_update_trampoline+0x16/0xa1
 ? tracing_gen_ctx+0x1c/0x1c
 __register_ftrace_function+0x93/0xb2
 ftrace_startup+0x21/0xf0
 ? tracing_gen_ctx+0x1c/0x1c
 register_ftrace_function_nolock+0x26/0x40
 register_ftrace_function+0x4e/0x143
 ? mutex_unlock+0x12/0x18
 ? tracing_gen_ctx+0x1c/0x1c
 function_trace_init+0x7d/0xc3
 tracer_init+0x23/0x2c
 tracing_set_tracer+0x1d5/0x206
 register_tracer+0x1c0/0x1e4
 init_function_trace+0x90/0x96
 early_trace_init+0x25c/0x352
 start_kernel+0x424/0x6e4
 x86_64_start_reservations+0x24/0x2a
 x86_64_start_kernel+0x8c/0x95
 secondary_startup_64_no_verify+0xe0/0xeb
 </TASK>
---[ end trace 0000000000000000 ]---


-- Steve