On Fri, Sep 06, 2024 at 04:48:28AM +0200, Jason A. Donenfeld wrote:
> On Thu, Sep 05, 2024 at 10:41:40PM +0200, Jason A. Donenfeld wrote:
> > On Thu, Sep 05, 2024 at 06:13:29PM +0200, Jason A. Donenfeld wrote:
> > > > +/*
> > > > + * The macro sets two stack frames, one for the caller and one for the
> > > > callee
> > > > + * because there are no requirement for the caller to set a stack
> > > > frame when
> > > > + * calling VDSO so it may have omitted to set one, especially on PPC64
> > > > + */
> > > > +
> > > > +.macro cvdso_call funct
> > > > + .cfi_startproc
> > > > + PPC_STLU r1, -PPC_MIN_STKFRM(r1)
> > > > + .cfi_adjust_cfa_offset PPC_MIN_STKFRM
> > > > + mflr r0
> > > > + PPC_STLU r1, -PPC_MIN_STKFRM(r1)
> > > > + .cfi_adjust_cfa_offset PPC_MIN_STKFRM
> > > > + PPC_STL r0, PPC_MIN_STKFRM + PPC_LR_STKOFF(r1)
> > > > + .cfi_rel_offset lr, PPC_MIN_STKFRM + PPC_LR_STKOFF
> > > > + get_datapage r8
> > > > + addi r8, r8, VDSO_RNG_DATA_OFFSET
> > > > + bl CFUNC(DOTSYM(\funct))
> > > > + PPC_LL r0, PPC_MIN_STKFRM + PPC_LR_STKOFF(r1)
> > > > + cmpwi r3, 0
> > > > + mtlr r0
> > > > + addi r1, r1, 2 * PPC_MIN_STKFRM
> > > > + .cfi_restore lr
> > > > + .cfi_def_cfa_offset 0
> > > > + crclr so
> > > > + bgelr+
> > > > + crset so
> > > > + neg r3, r3
> > > > + blr
> > > > + .cfi_endproc
> > > > +.endm
> > >
> > > Can you figure out what's going on and send a fix, which I'll squash
> > > into this commit?
> >
> > This doesn't work, but I wonder if something like it is what we want. I
> > need to head out for the day, but here's what I've got. It's all wrong
> > but might be of interest.
>
> Oh, I just got one small detail wrong before. The below actually works,
> and uses the same strategy as on arm64.
>
> Let me know if you'd like me to fix up this commit with the below patch,
> or if you have another way you'd like to go about it.
And here's the much shorter version in assembly, which maybe you prefer.
Also works, and is a bit less invasive than the other thing.
diff --git a/arch/powerpc/kernel/vdso/getrandom.S
b/arch/powerpc/kernel/vdso/getrandom.S
index a957cd2b2b03..070daba2d547 100644
--- a/arch/powerpc/kernel/vdso/getrandom.S
+++ b/arch/powerpc/kernel/vdso/getrandom.S
@@ -32,6 +32,14 @@
.cfi_rel_offset r2, PPC_MIN_STKFRM + STK_GOT
#endif
get_datapage r8
+#ifdef CONFIG_TIME_NS
+ lis r10, 0x7fff
+ ori r10, r10, 0xffff
+ lwz r9, VDSO_DATA_OFFSET + 4(r8)
+ cmpw r9, r10
+ bne +8
+ addi r8, r8, (1 << CONFIG_PAGE_SHIFT)
+#endif
addi r8, r8, VDSO_RNG_DATA_OFFSET
bl CFUNC(DOTSYM(\funct))
PPC_LL r0, PPC_MIN_STKFRM + PPC_LR_STKOFF(r1)
