From mboxrd@z Thu Jan 1 00:00:00 1970 From: Ingo Molnar Subject: Re: [PATCH] efi: fdt: avoid FDT manipulation after ExitBootServices() Date: Wed, 1 Feb 2017 20:03:41 +0100 Message-ID: <20170201190341.GA1060@gmail.com> References: <1485971102-23330-1-git-send-email-ard.biesheuvel@linaro.org> <1485971102-23330-2-git-send-email-ard.biesheuvel@linaro.org> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Return-path: Content-Disposition: inline In-Reply-To: <1485971102-23330-2-git-send-email-ard.biesheuvel-QSEj5FYQhm4dnm+yROfE0A@public.gmane.org> Sender: linux-efi-owner-u79uwXL29TY76Z2rM5mHXA@public.gmane.org To: Ard Biesheuvel Cc: leif.lindholm-QSEj5FYQhm4dnm+yROfE0A@public.gmane.org, mark.rutland-5wv7dgnIgG8@public.gmane.org, Thomas Gleixner , "H . Peter Anvin" , linux-arm-kernel-IAPFreCvJWM7uuMidbF8XUB+6BGkLq7r@public.gmane.org, riku.voipio-QSEj5FYQhm4dnm+yROfE0A@public.gmane.org, matt-mF/unelCI9GS6iBeEJttW/XRex20P6io@public.gmane.org, linux-kernel-u79uwXL29TY76Z2rM5mHXA@public.gmane.org, linux-efi-u79uwXL29TY76Z2rM5mHXA@public.gmane.org List-Id: linux-efi@vger.kernel.org * Ard Biesheuvel wrote: > Some AArch64 UEFI implementations disable the MMU in ExitBootServices(), > after which unaligned accesses to RAM are no longer supported. > > Commit abfb7b686a3e ("efi/libstub/arm*: Pass latest memory map to the > kernel") fixed an issue in the memory map handling of the stub FDT code, > but inadvertently created an issue with such firmwares, by moving some > of the FDT manipulation to after the invocation of ExitBootServices(). > Given that the stub's libfdt implementation uses the ordinary, accelerated > string functions, which rely on hardware handling of unaligned accesses, > manipulating the FDT with the MMU off may result in alignment faults. > > So fix the situation by moving the update_fdt_memmap() call into the > callback function invoked by efi_exit_boot_services() right before it > calls the ExitBootServices() UEFI service (which is arguably a better > place for it anyway) > > Note that disabling the MMU in ExitBootServices() is not compliant with > the UEFI spec, and carries great risk due to the fact that switching from > cached to uncached memory accesses halfway through compiler generated code > (i.e., involving a stack) can never be done in a way that is architecturally > safe. > > Cc: > Fixes: abfb7b686a3e ("efi/libstub/arm*: Pass latest memory map to the kernel") > Tested-by: Riku Voipio > Signed-off-by: Ard Biesheuvel > --- > drivers/firmware/efi/libstub/fdt.c | 14 +++----------- > 1 file changed, 3 insertions(+), 11 deletions(-) > > diff --git a/drivers/firmware/efi/libstub/fdt.c b/drivers/firmware/efi/libstub/fdt.c > index 921dfa047202..260c4b4b492e 100644 > --- a/drivers/firmware/efi/libstub/fdt.c > +++ b/drivers/firmware/efi/libstub/fdt.c > @@ -187,6 +187,7 @@ static efi_status_t update_fdt_memmap(void *fdt, struct efi_boot_memmap *map) > struct exit_boot_struct { > efi_memory_desc_t *runtime_map; > int *runtime_entry_count; > + void *new_fdt_addr; > }; > > static efi_status_t exit_boot_func(efi_system_table_t *sys_table_arg, > @@ -202,7 +203,7 @@ static efi_status_t exit_boot_func(efi_system_table_t *sys_table_arg, > efi_get_virtmap(*map->map, *map->map_size, *map->desc_size, > p->runtime_map, p->runtime_entry_count); > > - return EFI_SUCCESS; > + return update_fdt_memmap(p->new_fdt_addr, map); > } > > /* > @@ -300,22 +301,13 @@ efi_status_t allocate_new_fdt_and_exit_boot(efi_system_table_t *sys_table, > > priv.runtime_map = runtime_map; > priv.runtime_entry_count = &runtime_entry_count; > + priv.new_fdt_addr = (void *)*new_fdt_addr; Nit: could the type cast by dropped? Thanks, Ingo