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SubjectRe: [PATCH] riscv: Fix memblock reservation for device tree blob
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On Tue, 08 Oct 2019 16:31:17 PDT (-0700), aou@eecs.berkeley.edu wrote:
> On 2019-10-08 15:38:15 -0700, Palmer Dabbelt <palmer@sifive.com> wrote:
>> On Fri, 20 Sep 2019 21:34:57 PDT (-0700), anup@brainfault.org wrote:
>> > On Sat, Sep 21, 2019 at 6:30 AM Albert Ou <aou@eecs.berkeley.edu> wrote:
>> >>
>> >> This fixes an error with how the FDT blob is reserved in memblock.
>> >> An incorrect physical address calculation exposed the FDT header to
>> >> unintended corruption, which typically manifested with of_fdt_raw_init()
>> >> faulting during late boot after fdt_totalsize() returned a wrong value.
>> >> Systems with smaller physical memory sizes more frequently trigger this
>> >> issue, as the kernel is more likely to allocate from the DMA32 zone
>> >> where bbl places the DTB after the kernel image.
>> >>
>> >> Commit 671f9a3e2e24 ("RISC-V: Setup initial page tables in two stages")
>> >> changed the mapping of the DTB to reside in the fixmap area.
>> >> Consequently, early_init_fdt_reserve_self() cannot be used anymore in
>> >> setup_bootmem() since it relies on __pa() to derive a physical address,
>> >> which does not work with dtb_early_va that is no longer a valid kernel
>> >> logical address.
>> >>
>> >> The reserved[0x1] region shows the effect of the pointer underflow
>> >> resulting from the __pa(initial_boot_params) offset subtraction:
>> >>
>> >> [ 0.000000] MEMBLOCK configuration:
>> >> [ 0.000000] memory size = 0x000000001fe00000 reserved size = 0x0000000000a2e514
>> >> [ 0.000000] memory.cnt = 0x1
>> >> [ 0.000000] memory[0x0] [0x0000000080200000-0x000000009fffffff], 0x000000001fe00000 bytes flags: 0x0
>> >> [ 0.000000] reserved.cnt = 0x2
>> >> [ 0.000000] reserved[0x0] [0x0000000080200000-0x0000000080c2dfeb], 0x0000000000a2dfec bytes flags: 0x0
>> >> [ 0.000000] reserved[0x1] [0xfffffff080100000-0xfffffff080100527], 0x0000000000000528 bytes flags: 0x0
>> >>
>> >> With the fix applied:
>> >>
>> >> [ 0.000000] MEMBLOCK configuration:
>> >> [ 0.000000] memory size = 0x000000001fe00000 reserved size = 0x0000000000a2e514
>> >> [ 0.000000] memory.cnt = 0x1
>> >> [ 0.000000] memory[0x0] [0x0000000080200000-0x000000009fffffff], 0x000000001fe00000 bytes flags: 0x0
>> >> [ 0.000000] reserved.cnt = 0x2
>> >> [ 0.000000] reserved[0x0] [0x0000000080200000-0x0000000080c2dfeb], 0x0000000000a2dfec bytes flags: 0x0
>> >> [ 0.000000] reserved[0x1] [0x0000000080e00000-0x0000000080e00527], 0x0000000000000528 bytes flags: 0x0
>> >
>> > Thanks for catching this issue.
>> >
>> > Most of us did not notice this issue most likely because:
>> > 1. We generally have good enough RAM on QEMU and SiFive Unleashed
>> > 2. Most of people use OpenSBI FW_JUMP on QEMU and U-Boot on
>> > SiFive Unleashed to boot in Linux which places FDT quite far away
>> > from Linux kernel end
>> >
>> > Linux ARM64 kernel also uses FIXMAP to access FDT and over there
>> > as well early_init_fdt_reserve_self() is not used.
>> >
>> >>
>> >> Fixes: 671f9a3e2e24 ("RISC-V: Setup initial page tables in two stages")
>> >> Signed-off-by: Albert Ou <aou@eecs.berkeley.edu>
>> >> ---
>> >> arch/riscv/mm/init.c | 13 ++++++++++++-
>> >> 1 file changed, 12 insertions(+), 1 deletion(-)
>> >>
>> >> diff --git a/arch/riscv/mm/init.c b/arch/riscv/mm/init.c
>> >> index f0ba713..52d007c 100644
>> >> --- a/arch/riscv/mm/init.c
>> >> +++ b/arch/riscv/mm/init.c
>> >> @@ -11,6 +11,7 @@
>> >> #include <linux/swap.h>
>> >> #include <linux/sizes.h>
>> >> #include <linux/of_fdt.h>
>> >> +#include <linux/libfdt.h>
>> >>
>> >> #include <asm/fixmap.h>
>> >> #include <asm/tlbflush.h>
>> >> @@ -82,6 +83,8 @@ static void __init setup_initrd(void)
>> >> }
>> >> #endif /* CONFIG_BLK_DEV_INITRD */
>> >>
>> >> +static phys_addr_t __dtb_pa __initdata;
>> >
>> > May be dtb_early_pa will be more consistent name
>> > instead of __dtb_pa because it matches dtb_early_va
>> > used below.
>> >
>> >> +
>> >> void __init setup_bootmem(void)
>> >> {
>> >> struct memblock_region *reg;
>> >> @@ -117,7 +120,12 @@ void __init setup_bootmem(void)
>> >> setup_initrd();
>> >> #endif /* CONFIG_BLK_DEV_INITRD */
>> >>
>> >> - early_init_fdt_reserve_self();
>> >> + /*
>> >> + * Avoid using early_init_fdt_reserve_self() since __pa() does
>> >> + * not work for DTB pointers that are fixmap addresses
>> >> + */
>> >> + memblock_reserve(__dtb_pa, fdt_totalsize(dtb_early_va));
>> >> +
>> >> early_init_fdt_scan_reserved_mem();
>> >> memblock_allow_resize();
>> >> memblock_dump_all();
>> >> @@ -333,6 +341,7 @@ static uintptr_t __init best_map_size(phys_addr_t base, phys_addr_t size)
>> >> "not use absolute addressing."
>> >> #endif
>> >>
>> >> +
>> >
>> > Please remove this newline addition.
>> >
>> >> asmlinkage void __init setup_vm(uintptr_t dtb_pa)
>> >> {
>> >> uintptr_t va, end_va;
>> >> @@ -393,6 +402,8 @@ asmlinkage void __init setup_vm(uintptr_t dtb_pa)
>> >>
>> >> /* Save pointer to DTB for early FDT parsing */
>> >> dtb_early_va = (void *)fix_to_virt(FIX_FDT) + (dtb_pa & ~PAGE_MASK);
>> >> + /* Save physical address for memblock reservation */
>> >> + __dtb_pa = dtb_pa;
>> >> }
>> >>
>> >> static void __init setup_vm_final(void)
>> >> --
>> >> 2.7.4
>> >>
>> >>
>> >> _______________________________________________
>> >> linux-riscv mailing list
>> >> linux-riscv@lists.infradead.org
>> >> http://lists.infradead.org/mailman/listinfo/linux-riscv
>> >
>> > This deserves to be stable kernel fix as well.
>> > You should add:
>> > Cc: stable@vger.kernel.org
>> > in your commit description.
>> >
>> > Apart from minor nits above.
>> >
>> > Reviewed-by: Anup Patel <anup@brainfault.org>
>> >
>> > I tried this patch for both RV64 and RV32 on QEMU with
>> > Yocto rootfs.
>> >
>> > Tested-by: Anup Patel <anup@brainfault.org>
>> >
>> > Regards,
>> > Anup
>>
>> Albert: Do you plan on spinning a v2 of the patch set?
>>
>
> v2 was sent last week and has already been applied as
> 922b0375fc93fb1a20c5617e37c389c26bbccb70 by Paul.

Sorry about that.

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