Re: [PATCH] powerpc/chrp: Revert "Move PHB discovery" and "Make hydra_init() static"

[Christophe Leroy]

Christophe Leroy <christophe.leroy@xxxxxxxxxx> a écrit :

> Guenter Roeck <linux@xxxxxxxxxxxx> a écrit :
>
> > This patch reverts commit 407d418f2fd4 ("powerpc/chrp: Move PHB
> > discovery") and commit 9634afa67bfd ("powerpc/chrp: Make hydra_init()
> > static").
> >
> > Running the upstream kernel on Qemu's brand new "pegasos2" emulation
> > results in a variety of backtraces such as
> >
> > Kernel attempted to write user page (a1) - exploit attempt? (uid: 0)
> > ------------[ cut here ]------------
> > Bug: Write fault blocked by KUAP!
> > WARNING: CPU: 0 PID: 0 at arch/powerpc/mm/fault.c:230  
> > do_page_fault+0x4f4/0x920
> > CPU: 0 PID: 0 Comm: swapper Not tainted 5.13.2 #40
> > NIP:  c0021824 LR: c0021824 CTR: 00000000
> > REGS: c1085d50 TRAP: 0700   Not tainted  (5.13.2)
> > MSR:  00021032 <ME,IR,DR,RI>  CR: 24042254  XER: 00000000
> >
> > GPR00: c0021824 c1085e10 c0f8c520 00000021 3fffefff c1085c60  
> > c1085c58 00000000
> > GPR08: 00001032 00000000 00000000 c0ffb3ec 44042254 00000000  
> > 00000000 00000004
> > GPR16: 00000000 ffffffff 000000c4 000000d0 0188c6e0 01006000  
> > 00000001 40b14000
> > GPR24: c0ec000c 00000300 02000000 00000000 42000000 000000a1  
> > 00000000 c1085e60
> > NIP [c0021824] do_page_fault+0x4f4/0x920
> > LR [c0021824] do_page_fault+0x4f4/0x920
> > Call Trace:
> > [c1085e10] [c0021824] do_page_fault+0x4f4/0x920 (unreliable)
> > [c1085e50] [c0004254] DataAccess_virt+0xd4/0xe4
> >
> > and the system fails to boot. Bisect points to commit 407d418f2fd4
> > ("powerpc/chrp: Move PHB discovery"). Reverting this patch together with
> > commit 9634afa67bfd ("powerpc/chrp: Make hydra_init() static") fixes
> > the problem.
>
> Isn't there more than that in the backtrace ? If there is a fault  
> blocked by Kuap, it means there is a fault. It should be visible in  
> the traces.
>
> Should we fix the problem instead of reverting the commit that made  
> the problem visible ?

Also, as it is a KUAP fault, did you test without CONFIG_PPC_KUAP ?  
Does it boot ?

> > Cc: Oliver O'Halloran <oohall@xxxxxxxxx>
> > Cc: Geert Uytterhoeven <geert@xxxxxxxxxxxxxx>
> > Fixes: 407d418f2fd4 ("powerpc/chrp: Move PHB discovery")
> > Signed-off-by: Guenter Roeck <linux@xxxxxxxxxxxx>
> > ---
> > arch/powerpc/include/asm/hydra.h    |  2 ++
> > arch/powerpc/platforms/chrp/pci.c   | 11 ++---------
> > arch/powerpc/platforms/chrp/setup.c | 12 +++++++++++-
> > 3 files changed, 15 insertions(+), 10 deletions(-)
> >
> > diff --git a/arch/powerpc/include/asm/hydra.h  
> > b/arch/powerpc/include/asm/hydra.h
> > index d024447283a0..ae02eb53d6ef 100644
> > --- a/arch/powerpc/include/asm/hydra.h
> > +++ b/arch/powerpc/include/asm/hydra.h
> > @@ -94,6 +94,8 @@ extern volatile struct Hydra __iomem *Hydra;
> > #define HYDRA_INT_EXT7		18	/* Power Off Request */
> > #define HYDRA_INT_SPARE		19
> >
> > +extern int hydra_init(void);
> > +
> > #endif /* __KERNEL__ */
> >
> > #endif /* _ASMPPC_HYDRA_H */
> > diff --git a/arch/powerpc/platforms/chrp/pci.c  
> > b/arch/powerpc/platforms/chrp/pci.c
> > index 76e6256cb0a7..b2c2bf35b76c 100644
> > --- a/arch/powerpc/platforms/chrp/pci.c
> > +++ b/arch/powerpc/platforms/chrp/pci.c
> > @@ -131,7 +131,8 @@ static struct pci_ops rtas_pci_ops =
> >
> > volatile struct Hydra __iomem *Hydra = NULL;
> >
> > -static int __init hydra_init(void)
> > +int __init
> > +hydra_init(void)
> > {
> > 	struct device_node *np;
> > 	struct resource r;
> > @@ -313,14 +314,6 @@ chrp_find_bridges(void)
> > 		}
> > 	}
> > 	of_node_put(root);
> > -
> > -	/*
> > -	 *  "Temporary" fixes for PCI devices.
> > -	 *  -- Geert
> > -	 */
> > -	hydra_init();		/* Mac I/O */
> > -
> > -	pci_create_OF_bus_map();
> > }
> >
> > /* SL82C105 IDE Control/Status Register */
> > diff --git a/arch/powerpc/platforms/chrp/setup.c  
> > b/arch/powerpc/platforms/chrp/setup.c
> > index 3cfc382841e5..c45435aa5e36 100644
> > --- a/arch/powerpc/platforms/chrp/setup.c
> > +++ b/arch/powerpc/platforms/chrp/setup.c
> > @@ -334,11 +334,22 @@ static void __init chrp_setup_arch(void)
> > 	/* On pegasos, enable the L2 cache if not already done by OF */
> > 	pegasos_set_l2cr();
> >
> > +	/* Lookup PCI host bridges */
> > +	chrp_find_bridges();
> > +
> > +	/*
> > +	 *  Temporary fixes for PCI devices.
> > +	 *  -- Geert
> > +	 */
> > +	hydra_init();		/* Mac I/O */
> > +
> > 	/*
> > 	 *  Fix the Super I/O configuration
> > 	 */
> > 	sio_init();
> >
> > +	pci_create_OF_bus_map();
> > +
> > 	/*
> > 	 * Print the banner, then scroll down so boot progress
> > 	 * can be printed.  -- Cort
> > @@ -571,7 +582,6 @@ define_machine(chrp) {
> > 	.name			= "CHRP",
> > 	.probe			= chrp_probe,
> > 	.setup_arch		= chrp_setup_arch,
> > -	.discover_phbs		= chrp_find_bridges,
> > 	.init			= chrp_init2,
> > 	.show_cpuinfo		= chrp_show_cpuinfo,
> > 	.init_IRQ		= chrp_init_IRQ,
> > --
> > 2.25.1