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From: Joe Lawrence <joe.lawrence@redhat.com>
To: Josh Poimboeuf <jpoimboe@redhat.com>
Cc: Miroslav Benes <mbenes@suse.cz>,
	Gerald Schaefer <gerald.schaefer@de.ibm.com>,
	live-patching@vger.kernel.org, linux-kernel@vger.kernel.org,
	Peter Zijlstra <peterz@infradead.org>,
	Jessica Yu <jeyu@kernel.org>,
	linux-s390@vger.kernel.org, heiko.carstens@de.ibm.com,
	Vasily Gorbik <gor@linux.ibm.com>
Subject: Re: [PATCH v2 6/9] s390/module: Use s390_kernel_write() for late relocations
Date: Thu, 30 Apr 2020 10:38:21 -0400	[thread overview]
Message-ID: <20200430143821.GA10092@redhat.com> (raw)
In-Reply-To: <20200423181030.b5mircvgc7zmqacr@treble>

On Thu, Apr 23, 2020 at 01:10:30PM -0500, Josh Poimboeuf wrote:
> On Thu, Apr 23, 2020 at 09:12:28AM -0500, Josh Poimboeuf wrote:
> > > > this is strange. While I would have expected an exception similar to
> > > > this, it really should have happened on the "sturg" instruction which
> > > > does the DAT-off store in s390_kernel_write(), and certainly not with
> > > > an ID of 0004 (protection). However, in your case, it happens on a
> > > > normal store instruction, with 0004 indicating a protection exception.
> > > > 
> > > > This is more like what I would expect e.g. in the case where you do
> > > > _not_ use the s390_kernel_write() function for RO module text patching,
> > > > but rather normal memory access. So I am pretty sure that this is not
> > > > related to the s390_kernel_write(), but some other issue, maybe some
> > > > place left where you still use normal memory access?
> > > 
> > > The call trace above also suggests that it is not a late relocation, no? 
> > > The path is from KLP module init function through klp_enable_patch. It should 
> > > mean that the to-be-patched object is loaded (it must be a module thanks 
> > > to a check klp_init_object_loaded(), vmlinux relocations were processed 
> > > earlier in apply_relocations()).
> > > 
> > > However, the KLP module state here must be COMING, so s390_kernel_write() 
> > > should be used. What are we missing?
> > 
> > I'm also scratching my head.  It _should_ be using s390_kernel_write()
> > based on the module state, but I don't see that on the stack trace.
> > 
> > This trace (and Gerald's comment) seem to imply it's using
> > __builtin_memcpy(), which might expected for UNFORMED state.
> > 
> > Weird...
> 
> Mystery solved:
> 
>   $ CROSS_COMPILE=s390x-linux-gnu- scripts/faddr2line vmlinux apply_rela+0x16a/0x520
>   apply_rela+0x16a/0x520:
>   apply_rela at arch/s390/kernel/module.c:336
> 
> which corresponds to the following code in apply_rela():
> 
> 
> 	case R_390_PLTOFF64:	/* 16 bit offset from GOT to PLT. */
> 		if (info->plt_initialized == 0) {
> 			unsigned int *ip;
> 			ip = me->core_layout.base + me->arch.plt_offset +
> 				info->plt_offset;
> 			ip[0] = 0x0d10e310;	/* basr 1,0  */
> 			ip[1] = 0x100a0004;	/* lg	1,10(1) */
> 
> 
> Notice how it's writing directly to text... oops.
> 

This is more of note for the future, but when/if we add livepatch
support on arm64 we'll need to make the very same adjustment there as
well.  See the following pattern:

arch/arm64/kernel/module.c:

  reloc_insn_movw()
  reloc_insn_imm()
  reloc_insn_adrp()

    *place = cpu_to_le32(insn);

maybe something like aarch64_insn_patch_text_nosync() could be used
there, I dunno. (It looks like ftrace and jump_labels are using that
interface.)

This is outside the scope of the patchset, but I thought I'd mention it
as I was curious to see how other arches were currently handling their
relocation updates.

-- Joe


  parent reply	other threads:[~2020-04-30 14:38 UTC|newest]

Thread overview: 38+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2020-04-17 14:04 [PATCH v2 0/9] livepatch,module: Remove .klp.arch and module_disable_ro() Josh Poimboeuf
2020-04-17 14:04 ` [PATCH v2 1/9] livepatch: Disallow vmlinux.ko Josh Poimboeuf
2020-04-17 14:04 ` [PATCH v2 2/9] livepatch: Apply vmlinux-specific KLP relocations early Josh Poimboeuf
2020-04-20 17:57   ` Joe Lawrence
2020-04-20 18:25     ` Josh Poimboeuf
2020-04-20 19:01       ` Joe Lawrence
2020-04-20 19:11         ` Josh Poimboeuf
2020-04-20 19:49           ` Joe Lawrence
2020-04-20 19:51             ` Josh Poimboeuf
2020-04-23  1:10           ` Joe Lawrence
2020-04-21 11:54     ` Miroslav Benes
2020-04-17 14:04 ` [PATCH v2 3/9] livepatch: Remove .klp.arch Josh Poimboeuf
2020-04-17 14:04 ` [PATCH v2 4/9] livepatch: Prevent module-specific KLP rela sections from referencing vmlinux symbols Josh Poimboeuf
2020-04-17 14:04 ` [PATCH v2 5/9] s390: Change s390_kernel_write() return type to match memcpy() Josh Poimboeuf
2020-04-17 14:04 ` [PATCH v2 6/9] s390/module: Use s390_kernel_write() for late relocations Josh Poimboeuf
2020-04-22 12:28   ` Miroslav Benes
2020-04-24 13:43     ` Josh Poimboeuf
2020-04-22 14:40   ` Gerald Schaefer
2020-04-22 15:21     ` Gerald Schaefer
2020-04-22 19:46       ` Josh Poimboeuf
2020-04-23 12:33         ` Gerald Schaefer
2020-04-23 13:22           ` Miroslav Benes
2020-04-23 14:12             ` Josh Poimboeuf
2020-04-23 18:10               ` Josh Poimboeuf
2020-04-23 23:26                 ` Josh Poimboeuf
2020-04-24  2:35                   ` Joe Lawrence
2020-04-24  4:12                     ` Josh Poimboeuf
2020-04-24  7:20                   ` Christian Borntraeger
2020-04-24 13:37                     ` Josh Poimboeuf
2020-04-30 14:38                 ` Joe Lawrence [this message]
2020-04-30 16:48                   ` Josh Poimboeuf
2020-04-30 17:04                     ` Joe Lawrence
2020-04-23 14:21             ` Joe Lawrence
2020-04-17 14:04 ` [PATCH v2 7/9] x86/module: Use text_poke() " Josh Poimboeuf
2020-04-17 14:29   ` Peter Zijlstra
2020-04-17 14:51     ` Josh Poimboeuf
2020-04-17 14:04 ` [PATCH v2 8/9] livepatch: Remove module_disable_ro() usage Josh Poimboeuf
2020-04-17 14:04 ` [PATCH v2 9/9] module: Remove module_disable_ro() Josh Poimboeuf

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