On Thu, 22 Dec, at 11:23:39AM, Nicolai Stange wrote:
> With commit 4bc9f92e64c8 ("x86/efi-bgrt: Use efi_mem_reserve() to avoid
> copying image data"), efi_bgrt_init() calls into the memblock allocator
> through efi_mem_reserve() => efi_arch_mem_reserve() *after* mm_init()
> has been called.
>
> Indeed, KASAN reports a bad read access later on in
> efi_free_boot_services():
>
> BUG: KASAN: use-after-free in efi_free_boot_services+0xae/0x24c
> at addr ffff88022de12740
> Read of size 4 by task swapper/0/0
> page:ffffea0008b78480 count:0 mapcount:-127
> mapping: (null) index:0x1 flags: 0x5fff8000000000()
> [...]
> Call Trace:
> dump_stack+0x68/0x9f
> kasan_report_error+0x4c8/0x500
> kasan_report+0x58/0x60
> __asan_load4+0x61/0x80
> efi_free_boot_services+0xae/0x24c
> start_kernel+0x527/0x562
> x86_64_start_reservations+0x24/0x26
> x86_64_start_kernel+0x157/0x17a
> start_cpu+0x5/0x14
>
> The instruction at the given address is the first read from the memmap's
> memory, i.e. the read of md->type in efi_free_boot_services().
>
> Note that the writes earlier in efi_arch_mem_reserve() don't splat because
> they're done through early_memremap()ed addresses.
>
> So, after memblock is gone, allocations should be done through the "normal"
> page allocator. Introduce a helper, efi_memmap_alloc() for this. Use
> it from efi_arch_mem_reserve() and from efi_free_boot_services() as well.
>
> Fixes: 4bc9f92e64c8 ("x86/efi-bgrt: Use efi_mem_reserve() to avoid copying image data")
> Signed-off-by: Nicolai Stange <nicstange@xxxxxxxxx>
> ---
> arch/x86/platform/efi/quirks.c | 4 ++--
> drivers/firmware/efi/memmap.c | 38 ++++++++++++++++++++++++++++++++++++++
> include/linux/efi.h | 1 +
> 3 files changed, 41 insertions(+), 2 deletions(-)
Nice catch. Could you also modify efi_fake_memmap() to use your new
efi_memmap_alloc() function for consistency (note that all
memblock_alloc()s should probably be PAGE_SIZE aligned like the
fakemem code)?
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