On Thu, 22 Oct 2020 at 18:11, Russell King - ARM Linux admin <li...@armlinux.org.uk> wrote: > > On Thu, Oct 22, 2020 at 06:06:32PM +0200, Ard Biesheuvel wrote: > > On Thu, 22 Oct 2020 at 17:57, Dmitry Osipenko <dig...@gmail.com> wrote: > > > > > > 22.10.2020 10:06, Ard Biesheuvel пишет: > > > > On Thu, 22 Oct 2020 at 05:30, Kees Cook <keesc...@chromium.org> wrote: > > > >> > > > >> On Thu, Oct 22, 2020 at 03:00:06AM +0300, Dmitry Osipenko wrote: > > > >>> 22.10.2020 02:40, Kees Cook пишет: > > > >>>> On Thu, Oct 22, 2020 at 01:57:37AM +0300, Dmitry Osipenko wrote: > > > >>>>> The vfp_kmode_exception() function now is unreachable using relative > > > >>>>> branching in THUMB2 kernel configuration, resulting in a "relocation > > > >>>>> truncated to fit: R_ARM_THM_JUMP19 against symbol > > > >>>>> `vfp_kmode_exception'" > > > >>>>> linker error. Let's use long jump in order to fix the issue. > > > >>>> > > > >>>> Eek. Is this with gcc or clang? > > > >>> > > > >>> GCC 9.3.0 > > > >>> > > > >>>>> Fixes: eff8728fe698 ("vmlinux.lds.h: Add PGO and AutoFDO input > > > >>>>> sections") > > > >>>> > > > >>>> Are you sure it wasn't 512dd2eebe55 ("arm/build: Add missing > > > >>>> sections") ? > > > >>>> That commit may have implicitly moved the location of .vfp11_veneer, > > > >>>> though I thought I had chosen the correct position. > > > >>> > > > >>> I re-checked that the fixes tag is correct. > > > >>> > > > >>>>> Signed-off-by: Dmitry Osipenko <dig...@gmail.com> > > > >>>>> --- > > > >>>>> arch/arm/vfp/vfphw.S | 3 ++- > > > >>>>> 1 file changed, 2 insertions(+), 1 deletion(-) > > > >>>>> > > > >>>>> diff --git a/arch/arm/vfp/vfphw.S b/arch/arm/vfp/vfphw.S > > > >>>>> index 4fcff9f59947..6e2b29f0c48d 100644 > > > >>>>> --- a/arch/arm/vfp/vfphw.S > > > >>>>> +++ b/arch/arm/vfp/vfphw.S > > > >>>>> @@ -82,7 +82,8 @@ ENTRY(vfp_support_entry) > > > >>>>> ldr r3, [sp, #S_PSR] @ Neither lazy restore nor FP > > > >>>>> exceptions > > > >>>>> and r3, r3, #MODE_MASK @ are supported in kernel mode > > > >>>>> teq r3, #USR_MODE > > > >>>>> - bne vfp_kmode_exception @ Returns through lr > > > >>>>> + ldr r1, =vfp_kmode_exception > > > >>>>> + bxne r1 @ Returns through lr > > > >>>>> > > > >>>>> VFPFMRX r1, FPEXC @ Is the VFP enabled? > > > >>>>> DBGSTR1 "fpexc %08x", r1 > > > >>>> > > > >>>> This seems like a workaround though? I suspect the vfp11_veneer needs > > > >>>> moving? > > > >>>> > > > >>> > > > >>> I don't know where it needs to be moved. Please feel free to make a > > > >>> patch if you have a better idea, I'll be glad to test it. > > > >> > > > >> I might have just been distracted by the common "vfp" prefix. It's > > > >> possible that the text section shuffling just ended up being very > > > >> large, > > > >> so probably this patch is right then! > > > >> > > > > > > > > I already sent a fix for this issue: > > > > > > > > https://www.armlinux.org.uk/developer/patches/viewpatch.php?id=9018/1 > > > > > > > > > > The offending commit contains stable tag, so I assume that fixes tag is > > > mandatory. Yours patch misses the fixes tag. > > > > Russell, mind adding that? Or would you like me to update the patch in > > the patch system? > > Rather than adding the IT, I'm suggesting that we solve it a different > way - ensuring that the two bits of code are co-located. There's no > reason for them to be separated, and the assembly code entry point is > already called indirectly. > > The problem is the assembly ends up in the .text section which ends up > at the start of the binary, but depending on the compiler, functions > in .c files end up in their own sections. It would be good if, as > Dmitry has shown that it is indeed possible, to have them co-located. >
Why is that better? I provided a minimal fix which has zero impact on ARM builds, and minimal impact on Thumb2 builds, given that it retains the exact same semantics as before, but using a different opcode. R_ARM_THM_JUMP19 only has -/+ 1 MB range, i.e., smaller than the size of .text, and so using it for calls to external symbols is still going to be risky, unless we create a completely separate code section for VFP related routines. So we may need the IT instruction anyway, at which point we don't need anything more.