* [PATCH] x86/paravirt: Apply paravirt instructions in consistent order during boot/module load
@ 2022-03-07 18:03 Alex Thorlton
2022-03-07 18:45 ` Josh Poimboeuf
0 siblings, 1 reply; 3+ messages in thread
From: Alex Thorlton @ 2022-03-07 18:03 UTC (permalink / raw)
To: linux-kernel, x86
Cc: Alex Thorlton, Boris Ostrovsky, Thomas Gleixner, Ingo Molnar,
Borislav Petkov, Dave Hansen, H. Peter Anvin, Andrew Morton,
Peter Zijlstra, Josh Poimboeuf, Kefeng Wang, stable
Commit 4e6292114c74 ("x86/paravirt: Add new features for paravirt
patching") changed the order in which altinstructions and paravirt
instructions are patched at boot time. However, no analogous change was
made in module_finalize, where we apply altinstructions and
parainstructions during module load.
As a result, any code that generates "stacked up" altinstructions and
parainstructions (i.e. local_irq_save/restore) will produce different
results when used in built-in kernel code vs. kernel modules. This also
makes it possible to inadvertently replace altinstructions in the booted
kernel with their parainstruction counterparts when using
livepatch/kpatch.
To fix this, re-order the processing in module_finalize, so that we do
things in this order:
1. apply_paravirt
2. apply_retpolines
3. apply_alternatives
4. alternatives_smp_module_add
This is the same ordering that is used at boot time in
alternative_instructions.
Fixes: 4e6292114c74 ("x86/paravirt: Add new features for paravirt patching")
Signed-off-by: Alex Thorlton <alex.thorlton@oracle.com>
Reviewed-by: Boris Ostrovsky <boris.ostrovsky@oracle.com>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Ingo Molnar <mingo@redhat.com>
Cc: Borislav Petkov <bp@alien8.de>
Cc: Dave Hansen <dave.hansen@linux.intel.com>
Cc: "H. Peter Anvin" <hpa@zytor.com>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Josh Poimboeuf <jpoimboe@redhat.com>
Cc: Kefeng Wang <wangkefeng.wang@huawei.com>
Cc: x86@kernel.org
Cc: linux-kernel@vger.kernel.org
Cc: stable@vger.kernel.org # 5.13+
---
arch/x86/kernel/module.c | 9 ++++-----
1 file changed, 4 insertions(+), 5 deletions(-)
diff --git a/arch/x86/kernel/module.c b/arch/x86/kernel/module.c
index 95fa745e310a5..4edc9c87ad0bc 100644
--- a/arch/x86/kernel/module.c
+++ b/arch/x86/kernel/module.c
@@ -273,6 +273,10 @@ int module_finalize(const Elf_Ehdr *hdr,
retpolines = s;
}
+ if (para) {
+ void *pseg = (void *)para->sh_addr;
+ apply_paravirt(pseg, pseg + para->sh_size);
+ }
if (retpolines) {
void *rseg = (void *)retpolines->sh_addr;
apply_retpolines(rseg, rseg + retpolines->sh_size);
@@ -290,11 +294,6 @@ int module_finalize(const Elf_Ehdr *hdr,
tseg, tseg + text->sh_size);
}
- if (para) {
- void *pseg = (void *)para->sh_addr;
- apply_paravirt(pseg, pseg + para->sh_size);
- }
-
/* make jump label nops */
jump_label_apply_nops(me);
--
2.33.1
^ permalink raw reply related [flat|nested] 3+ messages in thread
* Re: [PATCH] x86/paravirt: Apply paravirt instructions in consistent order during boot/module load
2022-03-07 18:03 [PATCH] x86/paravirt: Apply paravirt instructions in consistent order during boot/module load Alex Thorlton
@ 2022-03-07 18:45 ` Josh Poimboeuf
2022-03-07 19:02 ` Alex Thorlton
0 siblings, 1 reply; 3+ messages in thread
From: Josh Poimboeuf @ 2022-03-07 18:45 UTC (permalink / raw)
To: Alex Thorlton
Cc: linux-kernel, x86, Boris Ostrovsky, Thomas Gleixner, Ingo Molnar,
Borislav Petkov, Dave Hansen, H. Peter Anvin, Andrew Morton,
Peter Zijlstra, Kefeng Wang, stable
On Mon, Mar 07, 2022 at 12:03:38PM -0600, Alex Thorlton wrote:
> Commit 4e6292114c74 ("x86/paravirt: Add new features for paravirt
> patching") changed the order in which altinstructions and paravirt
> instructions are patched at boot time. However, no analogous change was
> made in module_finalize, where we apply altinstructions and
> parainstructions during module load.
>
> As a result, any code that generates "stacked up" altinstructions and
> parainstructions (i.e. local_irq_save/restore) will produce different
> results when used in built-in kernel code vs. kernel modules. This also
> makes it possible to inadvertently replace altinstructions in the booted
> kernel with their parainstruction counterparts when using
> livepatch/kpatch.
>
> To fix this, re-order the processing in module_finalize, so that we do
> things in this order:
>
> 1. apply_paravirt
> 2. apply_retpolines
> 3. apply_alternatives
> 4. alternatives_smp_module_add
>
> This is the same ordering that is used at boot time in
> alternative_instructions.
>
> Fixes: 4e6292114c74 ("x86/paravirt: Add new features for paravirt patching")
> Signed-off-by: Alex Thorlton <alex.thorlton@oracle.com>
> Reviewed-by: Boris Ostrovsky <boris.ostrovsky@oracle.com>
Peter previously posted a fix, buried in his IBT series:
https://lkml.kernel.org/r/20220303112825.068773913@infradead.org
It should probably go ahead and be merged now...
--
Josh
^ permalink raw reply [flat|nested] 3+ messages in thread
* Re: [PATCH] x86/paravirt: Apply paravirt instructions in consistent order during boot/module load
2022-03-07 18:45 ` Josh Poimboeuf
@ 2022-03-07 19:02 ` Alex Thorlton
0 siblings, 0 replies; 3+ messages in thread
From: Alex Thorlton @ 2022-03-07 19:02 UTC (permalink / raw)
To: Josh Poimboeuf
Cc: Alex Thorlton, linux-kernel, x86, Boris Ostrovsky,
Thomas Gleixner, Ingo Molnar, Borislav Petkov, Dave Hansen,
H. Peter Anvin, Andrew Morton, Peter Zijlstra, Kefeng Wang,
stable
On Mon, Mar 07, 2022 at 10:45:05AM -0800, Josh Poimboeuf wrote:
> On Mon, Mar 07, 2022 at 12:03:38PM -0600, Alex Thorlton wrote:
> > Commit 4e6292114c74 ("x86/paravirt: Add new features for paravirt
> > patching") changed the order in which altinstructions and paravirt
> > instructions are patched at boot time. However, no analogous change was
> > made in module_finalize, where we apply altinstructions and
> > parainstructions during module load.
> >
> > As a result, any code that generates "stacked up" altinstructions and
> > parainstructions (i.e. local_irq_save/restore) will produce different
> > results when used in built-in kernel code vs. kernel modules. This also
> > makes it possible to inadvertently replace altinstructions in the booted
> > kernel with their parainstruction counterparts when using
> > livepatch/kpatch.
> >
> > To fix this, re-order the processing in module_finalize, so that we do
> > things in this order:
> >
> > 1. apply_paravirt
> > 2. apply_retpolines
> > 3. apply_alternatives
> > 4. alternatives_smp_module_add
> >
> > This is the same ordering that is used at boot time in
> > alternative_instructions.
> >
> > Fixes: 4e6292114c74 ("x86/paravirt: Add new features for paravirt patching")
> > Signed-off-by: Alex Thorlton <alex.thorlton@oracle.com>
> > Reviewed-by: Boris Ostrovsky <boris.ostrovsky@oracle.com>
>
> Peter previously posted a fix, buried in his IBT series:
>
> https://urldefense.com/v3/__https://lkml.kernel.org/r/20220303112825.068773913@infradead.org__;!!ACWV5N9M2RV99hQ!YARvXhahbleGAt689pqTXJU7ko-rePIjzrbuGmemJXgFRViFZ8FDfOy7mHZQ7CPaG6Y$
>
> It should probably go ahead and be merged now...
Ahh, yep - hadn't seen that one yet! In any case, I'm glad this is on
other folk's radar.
Thanks for letting me know, Josh!
- Alex
^ permalink raw reply [flat|nested] 3+ messages in thread
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2022-03-07 18:03 [PATCH] x86/paravirt: Apply paravirt instructions in consistent order during boot/module load Alex Thorlton
2022-03-07 18:45 ` Josh Poimboeuf
2022-03-07 19:02 ` Alex Thorlton
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