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h=Date:Subject:From:To:Cc:References:In-Reply-To:From; b=aPE16gPYY9PUw/fxzqTkP+lcnDIV/b3a+mRw82J4LzhDjjcRpZiFgFBcfB/B96oIh gCO0T5lhBi49FXApUtRjoL352Ho5kf9eO9zToilW3bK1SZwjjaYOEeZ804gTnNxlVL qbeQ3+uBHXS34yLYK9MToNou9KG1wtlQfcdQPi4bdWF0byxqoytewUaPXc8e4x+WQz 3HFWMvS5O00IEk+v3OfyU05LzpIWU/g+id987hDmrD6oTfwVFpF0dY4W9ZjtMRy5rF D3iHYRbPyLf90WPTDtkMRcWA2vMHhVysxD2bsCwnFAbgc0zvdRMhhCvXbf2rGRXjbq XHJ/HRk6mqBow== Message-ID: Date: Mon, 14 Jul 2025 23:50:57 -0700 Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v1 1/1] x86/fred: Remove ENDBR64 from FRED entry points From: Xin Li To: linux-kernel@vger.kernel.org Cc: luto@kernel.org, tglx@linutronix.de, mingo@redhat.com, bp@alien8.de, dave.hansen@linux.intel.com, x86@kernel.org, hpa@zytor.com, jmill@asu.edu, peterz@infradead.org, andrew.cooper3@citrix.com References: <20250715064437.807569-1-xin@zytor.com> Content-Language: en-US Autocrypt: addr=xin@zytor.com; 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charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit On 7/14/2025 11:44 PM, Xin Li (Intel) wrote: > The FRED specification v9.0 states that there is no need for FRED > event handlers to begin with ENDBR64, because in the presence of > supervisor indirect branch tracking, FRED event delivery does not > enter the WAIT_FOR_ENDBRANCH state. > > As a result, remove ENDBR64 from FRED entry points. > > Then add ANNOTATE_NOENDBR to indicate that FRED entry points will > never be used for indirect calls to suppress an objtool warning. > > This change implies that any indirect CALL/JMP to FRED entry points > causes #CP in the presence of supervisor indirect branch tracking. > > Credit goes to Jennifer Miller and other contributors > from Arizona State University whose work led to this change. > > Link: https://lore.kernel.org/linux-hardening/Z60NwR4w%2F28Z7XUa@ubun/ > Reviewed-by: H. Peter Anvin (Intel) > Signed-off-by: Xin Li (Intel) > Cc: Jennifer Miller > Cc: Peter Zijlstra > Cc: Andrew Cooper > Cc: H. Peter Anvin Sorry, forgot to put CC stable. > --- > arch/x86/entry/entry_64_fred.S | 2 +- > 1 file changed, 1 insertion(+), 1 deletion(-) > > diff --git a/arch/x86/entry/entry_64_fred.S b/arch/x86/entry/entry_64_fred.S > index 29c5c32c16c3..907bd233c6c1 100644 > --- a/arch/x86/entry/entry_64_fred.S > +++ b/arch/x86/entry/entry_64_fred.S > @@ -16,7 +16,7 @@ > > .macro FRED_ENTER > UNWIND_HINT_END_OF_STACK > - ENDBR > + ANNOTATE_NOENDBR > PUSH_AND_CLEAR_REGS > movq %rsp, %rdi /* %rdi -> pt_regs */ > .endm