From mboxrd@z Thu Jan 1 00:00:00 1970 From: will.deacon@arm.com (Will Deacon) Date: Fri, 29 Jul 2016 11:57:47 +0100 Subject: [PATCH] arm64: vmlinux.lds: make __rela_offset and __dynsym_offset ABSOLUTE In-Reply-To: References: <1469715314-23260-1-git-send-email-ard.biesheuvel@linaro.org> <20160729090634.GA16593@arm.com> <20160729104947.GE16593@arm.com> Message-ID: <20160729105747.GF16593@arm.com> To: linux-arm-kernel@lists.infradead.org List-Id: linux-arm-kernel.lists.infradead.org On Fri, Jul 29, 2016 at 12:52:12PM +0200, Ard Biesheuvel wrote: > On 29 July 2016 at 12:49, Will Deacon wrote: > > On Fri, Jul 29, 2016 at 12:46:49PM +0200, Ard Biesheuvel wrote: > >> On 29 July 2016 at 11:30, Ard Biesheuvel wrote: > >> > On 29 July 2016 at 11:06, Will Deacon wrote: > >> >> Hi Ard, > >> >> > >> >> On Thu, Jul 28, 2016 at 04:15:14PM +0200, Ard Biesheuvel wrote: > >> >>> Due to the untyped KIMAGE_VADDR constant, the linker may not notice > >> >>> that the __rela_offset and __dynsym_offset expressions are absolute > >> >>> values (i.e., are not subject to relocation). This does not matter for > >> >>> KASLR, but it does confuse kallsyms in relative mode, since it uses > >> >>> the lowest non-absolute symbol address as the anchor point, and expects > >> >>> all other symbol addresses to be within 4 GB of it. > >> >>> > >> >>> Fix this by qualifying these expressions as ABSOLUTE() explicitly. > >> >>> > >> >>> Fixes: 0cd3defe0af4 ("arm64: kernel: perform relocation processing from ID map") > >> >>> Signed-off-by: Ard Biesheuvel > >> >>> --- > >> >>> arch/arm64/kernel/vmlinux.lds.S | 4 ++-- > >> >>> 1 file changed, 2 insertions(+), 2 deletions(-) > >> >>> > >> >>> diff --git a/arch/arm64/kernel/vmlinux.lds.S b/arch/arm64/kernel/vmlinux.lds.S > >> >>> index 89d6e177ecbd..d49492179967 100644 > >> >>> --- a/arch/arm64/kernel/vmlinux.lds.S > >> >>> +++ b/arch/arm64/kernel/vmlinux.lds.S > >> >>> @@ -184,9 +184,9 @@ SECTIONS > >> >>> *(.hash) > >> >>> } > >> >>> > >> >>> - __rela_offset = ADDR(.rela) - KIMAGE_VADDR; > >> >>> + __rela_offset = ABSOLUTE(ADDR(.rela) - KIMAGE_VADDR); > >> >>> __rela_size = SIZEOF(.rela); > >> >>> - __dynsym_offset = ADDR(.dynsym) - KIMAGE_VADDR; > >> >>> + __dynsym_offset = ABSOLUTE(ADDR(.dynsym) - KIMAGE_VADDR); > >> >> > >> >> You removed the __dynsym_offset entry entirely in "arm64: relocatable: > >> >> suppress R_AARCH64_ABS64 relocations in vmlinux", so I'll drop this part > >> >> of the patch and assume you'll do a separate backport for stable. Ok? > >> >> > >> > > >> > If you are ok with fixing up patches manually while applying, could we > >> > just reorder them instead? > >> > >> Actually, this should go into v4.8-late not -stable > > > > Then the fixes tag is pretty confusing, since that's a commit from v4.7. > > > > Sorry, my bad. I managed to confuse myself here. > The tag is accurate, I was wrong. This should go into v4.7 as well. Haha, ok! So if this is v4.7 material, what *should* the fixes tag be? > Note that the breakage I experienced was only with an LD built from > binutils-gdb HEAD (2.28), so I guess there is no urgency here. Sure, but people might upgrade their binutils before their kernel Image, so the backport is worthwhile. Will