On Mon, Dec 16, 2024 at 12:26:58PM +0800, Ruihan Li wrote: > Currently, EFI services can be used after they are exited because we > allocate memory after exiting EFI services. > > An example call stack is: > > grub_multiboot_boot > grub_multiboot2_make_mbi > grub_efi_finish_boot_services > b->exit_boot_services > normal_boot > grub_relocator32_boot > grub_relocator_alloc_chunk_align_safe > grub_relocator_alloc_chunk_align > grub_malloc > grub_memalign > grub_mm_add_region_fn > [= grub_efi_mm_add_regions] > grub_efi_allocate_any_pages > grub_efi_allocate_pages_real > b->allocate_pages > > This can lead to confusing errors. After exiting EFI services, > b->allocate_pages may point to the NULL address, resulting in something > like: > > !!!! X64 Exception Type - 01(#DB - Debug) CPU Apic ID - 00000000 !!!! > RIP - 000000000000201F, CS - 0000000000000038, RFLAGS - 0000000000200002 > RAX - 000000007F9EE010, RCX - 0000000000000001, RDX - 0000000000000002 > RBX - 0000000000000006, RSP - 00000000001CFBEC, RBP - 0000000000000000 > RSI - 0000000000000000, RDI - 00000000FFFFFFFF > R8 - 0000000000000006, R9 - 000000007FEDFFB8, R10 - 0000000000000000 > R11 - 0000000000000475, R12 - 0000000000000001, R13 - 0000000000000002 > R14 - 00000000FFFFFFFF, R15 - 000000007E432C08 > DS - 0000000000000030, ES - 0000000000000030, FS - 0000000000000030 > GS - 0000000000000030, SS - 0000000000000030 > CR0 - 0000000080010033, CR2 - 0000000000000000, CR3 - 000000007FC01000 > CR4 - 0000000000000668, CR8 - 0000000000000000 > DR0 - 0000000000000000, DR1 - 0000000000000000, DR2 - 0000000000000000 > DR3 - 0000000000000000, DR6 - 00000000FFFF0FF0, DR7 - 0000000000000400 > GDTR - 000000007F9DE000 0000000000000047, LDTR - 0000000000000000 > IDTR - 000000007F470018 0000000000000FFF, TR - 0000000000000000 > FXSAVE_STATE - 00000000001CF840 > > Ideally, we would like to avoid all memory allocations after exiting EFI > services altogether, but that requires significant code changes. This > patch suggests a simple workaround that resets grub_mm_add_region_fn > after exiting EFI services, so: > > - Memory allocations after exiting EFI services have a better chance of > success because grub_memalign will try to reclaim the disk cache if > it sees a NULL grub_mm_add_region_fn. > > - At worst, it will fail to allocate memory after exiting EFI services, > but it will explicitly tell users that it's out of memory, which is > still much better than the current situation where it fails in a > fairly random way and triggers a CPU exception. > > Signed-off-by: Ruihan Li <lrh2...@pku.edu.cn>
Reviewed-by: Daniel Kiper <daniel.ki...@oracle.com> However, should not we go further and extend the heap with additional memory before EBS? 1 MiB? Daniel _______________________________________________ Grub-devel mailing list Grub-devel@gnu.org https://lists.gnu.org/mailman/listinfo/grub-devel
