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[198.145.64.163]) by smtp.gmail.com with ESMTPSA id s137sm2480478pfs.45.2020.03.26.13.39.04 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Thu, 26 Mar 2020 13:39:04 -0700 (PDT) Date: Thu, 26 Mar 2020 13:39:03 -0700 From: Kees Cook To: Borislav Petkov Cc: "H.J. Lu" , linux-kernel@vger.kernel.org, Andy Lutomirski , Thomas Gleixner , Thomas Lendacky , Sami Tolvanen , Heiko Carstens , Ingo Molnar , "H . Peter Anvin" , x86@kernel.org, Arnd Bergmann , linux-arch@vger.kernel.org, Yu-cheng Yu Subject: Re: [PATCH 1/2] Add RUNTIME_DISCARD_EXIT to generic DISCARDS Message-ID: <202003261335.CC263EF@keescook> References: <20200326193021.255002-1-hjl.tools@gmail.com> <20200326201142.GJ11398@zn.tnic> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20200326201142.GJ11398@zn.tnic> Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Thu, Mar 26, 2020 at 09:11:42PM +0100, Borislav Petkov wrote: > On Thu, Mar 26, 2020 at 12:30:20PM -0700, H.J. Lu wrote: > > In x86 kernel, .exit.text and .exit.data sections are discarded at > > runtime, not by linker. Add RUNTIME_DISCARD_EXIT to generic DISCARDS > > and define it in x86 kernel linker script to keep them. > > > > Signed-off-by: H.J. Lu > > Reviewed-by: Kees Cook > > --- > > arch/x86/kernel/vmlinux.lds.S | 1 + > > include/asm-generic/vmlinux.lds.h | 10 ++++++++-- > > 2 files changed, 9 insertions(+), 2 deletions(-) > > > > diff --git a/arch/x86/kernel/vmlinux.lds.S b/arch/x86/kernel/vmlinux.lds.S > > index e3296aa028fe..7206e1ac23dd 100644 > > --- a/arch/x86/kernel/vmlinux.lds.S > > +++ b/arch/x86/kernel/vmlinux.lds.S > > @@ -21,6 +21,7 @@ > > #define LOAD_OFFSET __START_KERNEL_map > > #endif > > > > +#define RUNTIME_DISCARD_EXIT > > #define EMITS_PT_NOTE > > #define RO_EXCEPTION_TABLE_ALIGN 16 > > > > diff --git a/include/asm-generic/vmlinux.lds.h b/include/asm-generic/vmlinux.lds.h > > index e00f41aa8ec4..6b943fb8c5fd 100644 > > --- a/include/asm-generic/vmlinux.lds.h > > +++ b/include/asm-generic/vmlinux.lds.h > > @@ -894,10 +894,16 @@ > > * section definitions so that such archs put those in earlier section > > * definitions. > > */ > > +#ifdef RUNTIME_DISCARD_EXIT > > +#define EXIT_DISCARDS > > +#else > > +#define EXIT_DISCARDS \ > > + EXIT_TEXT \ > > + EXIT_DATA > > +#endif > > /me goes back and reads the old thread on this... > > Kees, do you expect other arches to actually need this > RUNTIME_DISCARD_EXIT thing or was that a hypothetical thing? > > /me searches more... > > oh, there's a patchset from you > > https://lkml.kernel.org/r/20200228002244.15240-1-keescook@chromium.org > > which already contains this patch *and* an ARM64 patch which defines > RUNTIME_DISCARD_EXIT so I'm guessing ARM64 wants to discard at runtime > too. Correct. > Which leaves the question why is H.J. sending that patch separate and > you carry it in a patchset about orphan section warning? Seems like it > wants to be in your patchset? I had needed the same clean up for the orphan section handling, and since it hadn't been picked up yet, I included it in my series. I'm still stuck addressing several review comments, so there's no reason to wait for me: I can easily rebase once these patches land somewhere. I'd be happy to see them in -tip. Thanks! -Kees -- Kees Cook