• Josh Poimboeuf's avatar
    module: Fix livepatch/ftrace module text permissions race · 2d1a9468
    Josh Poimboeuf authored
    [ Upstream commit 9f255b632bf12c4dd7fc31caee89aa991ef75176 ]
    
    It's possible for livepatch and ftrace to be toggling a module's text
    permissions at the same time, resulting in the following panic:
    
      BUG: unable to handle page fault for address: ffffffffc005b1d9
      #PF: supervisor write access in kernel mode
      #PF: error_code(0x0003) - permissions violation
      PGD 3ea0c067 P4D 3ea0c067 PUD 3ea0e067 PMD 3cc13067 PTE 3b8a1061
      Oops: 0003 [#1] PREEMPT SMP PTI
      CPU: 1 PID: 453 Comm: insmod Tainted: G           O  K   5.2.0-rc1-a188339ca5 #1
      Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS 1.12.0-20181126_142135-anatol 04/01/2014
      RIP: 0010:apply_relocate_add+0xbe/0x14c
      Code: fa 0b 74 21 48 83 fa 18 74 38 48 83 fa 0a 75 40 eb 08 48 83 38 00 74 33 eb 53 83 38 00 75 4e 89 08 89 c8 eb 0a 83 38 00 75 43 <89> 08 48 63 c1 48 39 c8 74 2e eb 48 83 38 00 75 32 48 29 c1 89 08
      RSP: 0018:ffffb223c00dbb10 EFLAGS: 00010246
      RAX: ffffffffc005b1d9 RBX: 0000000000000000 RCX: ffffffff8b200060
      RDX: 000000000000000b RSI: 0000004b0000000b RDI: ffff96bdfcd33000
      RBP: ffffb223c00dbb38 R08: ffffffffc005d040 R09: ffffffffc005c1f0
      R10: ffff96bdfcd33c40 R11: ffff96bdfcd33b80 R12: 0000000000000018
      R13: ffffffffc005c1f0 R14: ffffffffc005e708 R15: ffffffff8b2fbc74
      FS:  00007f5f447beba8(0000) GS:ffff96bdff900000(0000) knlGS:0000000000000000
      CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
      CR2: ffffffffc005b1d9 CR3: 000000003cedc002 CR4: 0000000000360ea0
      DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
      DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
      Call Trace:
       klp_init_object_loaded+0x10f/0x219
       ? preempt_latency_start+0x21/0x57
       klp_enable_patch+0x662/0x809
       ? virt_to_head_page+0x3a/0x3c
       ? kfree+0x8c/0x126
       patch_init+0x2ed/0x1000 [livepatch_test02]
       ? 0xffffffffc0060000
       do_one_initcall+0x9f/0x1c5
       ? kmem_cache_alloc_trace+0xc4/0xd4
       ? do_init_module+0x27/0x210
       do_init_module+0x5f/0x210
       load_module+0x1c41/0x2290
       ? fsnotify_path+0x3b/0x42
       ? strstarts+0x2b/0x2b
       ? kernel_read+0x58/0x65
       __do_sys_finit_module+0x9f/0xc3
       ? __do_sys_finit_module+0x9f/0xc3
       __x64_sys_finit_module+0x1a/0x1c
       do_syscall_64+0x52/0x61
       entry_SYSCALL_64_after_hwframe+0x44/0xa9
    
    The above panic occurs when loading two modules at the same time with
    ftrace enabled, where at least one of the modules is a livepatch module:
    
    CPU0					CPU1
    klp_enable_patch()
      klp_init_object_loaded()
        module_disable_ro()
        					ftrace_module_enable()
    					  ftrace_arch_code_modify_post_process()
    				    	    set_all_modules_text_ro()
          klp_write_object_relocations()
            apply_relocate_add()
    	  *patches read-only code* - BOOM
    
    A similar race exists when toggling ftrace while loading a livepatch
    module.
    
    Fix it by ensuring that the livepatch and ftrace code patching
    operations -- and their respective permissions changes -- are protected
    by the text_mutex.
    
    Link: http://lkml.kernel.org/r/ab43d56ab909469ac5d2520c5d944ad6d4abd476.1560474114.git.jpoimboe@redhat.comReported-by: default avatarJohannes Erdfelt <johannes@erdfelt.com>
    Fixes: 444d13ff ("modules: add ro_after_init support")
    Acked-by: default avatarJessica Yu <jeyu@kernel.org>
    Reviewed-by: default avatarPetr Mladek <pmladek@suse.com>
    Reviewed-by: default avatarMiroslav Benes <mbenes@suse.cz>
    Signed-off-by: default avatarJosh Poimboeuf <jpoimboe@redhat.com>
    Signed-off-by: default avatarSteven Rostedt (VMware) <rostedt@goodmis.org>
    Signed-off-by: default avatarSasha Levin <sashal@kernel.org>
    2d1a9468
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