On 02/23/17 11:54, Frank Rowand wrote: > On 02/13/17 18:50, Stephen Boyd wrote: >> The 'blob' we pass into populate_properties() is marked as const, >> but we cast that const away when we assign the result of >> fdt_getprop_by_offset() to pp->value. Let's mark value as const >> instead, so that code can't mistakenly write to the value of the >> property that we've so far advertised as const. >> >> Unfortunately, this exposes a problem with the fdt resolver code, >> where we overwrite the value member of properties of phandles to >> update them with their final value. Add a comment for now to >> indicate where we're potentially writing over const data. > > The resolver should not be over writing anything in the FDT. I'll > look at what is going on there. OK, now that I have looked at the resolver, I see that you meant that the resolver code is modifying the _overlay_ FDT, not the FDT that was used at initial boot. So not what I thought you meant. I'll reply separately to the original patch email with a more complete response. -Frank > > The FDT we expose to user space should be the FDT we booted with, > not something later modified. > > -Frank > >> >> You can see the problem here by loading an overlay dtb into >> the kernel via the request firmware helper method (not direct >> loading) and then passing that tree to the resolver on an arm64 >> device. In this case, the firmware data is vmapped with KERNEL_PAGE_RO >> and the code crashes when attempting to write to the blob to update >> the phandle properties. >> >> Signed-off-by: Stephen Boyd <stephen.boyd@xxxxxxxxxx> >> --- >> >> I was thinking perhaps it would work to store another __be32 variant >> of the phandle in each device node, but then we still have a problem >> with properties that have phandles inside them at some offset that we >> need to update. I guess the only real solution is to deep copy the >> property in that case and then save around some info to free the >> duplicated property later on? >> >> drivers/of/base.c | 2 +- >> drivers/of/fdt.c | 12 ++++++------ >> drivers/of/resolver.c | 3 +++ >> include/linux/of.h | 2 +- >> 4 files changed, 11 insertions(+), 8 deletions(-) > > < snip > > -- To unsubscribe from this list: send the line "unsubscribe devicetree" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
