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Re: [PATCH] livepatch: account for patch offset when applying NOP patch
- To: Roger Pau Monné <roger.pau@xxxxxxxxxx>
- From: Jan Beulich <jbeulich@xxxxxxxx>
- Date: Wed, 30 Mar 2022 12:43:48 +0200
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- Cc: "xen-devel@xxxxxxxxxxxxxxxxxxxx" <xen-devel@xxxxxxxxxxxxxxxxxxxx>, Ross Lagerwall <ross.lagerwall@xxxxxxxxxx>, Konrad Wilk <konrad.wilk@xxxxxxxxxx>, Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
- Delivery-date: Wed, 30 Mar 2022 10:43:54 +0000
- List-id: Xen developer discussion <xen-devel.lists.xenproject.org>
On 30.03.2022 12:19, Roger Pau Monné wrote:
> On Wed, Mar 30, 2022 at 10:03:11AM +0200, Jan Beulich wrote:
>> While not triggered by the trivial xen_nop in-tree patch on
>> staging/master, that patch exposes a problem on the stable trees, where
>> all functions have ENDBR inserted. When NOP-ing out a range, we need to
>> account for this. Handle this right in livepatch_insn_len().
>>
>> Fixes: 6974c75180f1 ("xen/x86: Livepatch: support patching CET-enhanced
>> functions")
>> Signed-off-by: Jan Beulich <jbeulich@xxxxxxxx>
>> ---
>> Only build tested, as I don't have a live patching environment available.
>>
>> For Arm this assumes that the patch_offset field starts out as zero; I
>> think we can make such an assumption, yet otoh on x86 explicit
>> initialization was added by the cited commit.
>>
>> --- a/xen/include/xen/livepatch.h
>> +++ b/xen/include/xen/livepatch.h
>> @@ -90,7 +90,7 @@ static inline
>> unsigned int livepatch_insn_len(const struct livepatch_func *func)
>> {
>> if ( !func->new_addr )
>> - return func->new_size;
>> + return func->new_size - func->patch_offset;
>>
>> return ARCH_PATCH_INSN_SIZE;
>> }
>
> Don't you also need to move the call to livepatch_insn_len() in
> arch_livepatch_apply() after func->patch_offset has been adjusted to
> account for ENDBR presence?
Oh, yes, I definitely need to.
Jan
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