6.8-stable review patch. If anyone has any objections, please let me know.
------------------
From: Ard Biesheuvel ardb@kernel.org
commit d21f5a59ea773826cc489acb287811d690b703cc upstream.
The pure EFI stub entry point does not take a struct boot_params from the boot loader, but creates it from scratch, and populates only the fields that still have meaning in this context (command line, initrd base and size, etc)
The original mixed mode implementation used the EFI handover protocol instead, where the boot loader (i.e., GRUB) populates a boot_params struct and passes it to a special Linux specific EFI entry point that takes the boot_params pointer as its third argument.
When the new mixed mode implementation was introduced, using a special 32-bit PE entrypoint in the 64-bit kernel, it adopted the pure approach, and relied on the EFI stub to create the struct boot_params. This is preferred because it makes the bootloader side much easier to implement, as it does not need any x86-specific knowledge on how struct boot_params and struct setup_header are put together. This mixed mode implementation was adopted by systemd-boot version 252 and later.
When commit
e2ab9eab324c ("x86/boot/compressed: Move 32-bit entrypoint code into .text section")
refactored this code and moved it out of head_64.S, the fact that ESI was populated with the address of the base of the image was overlooked, and to simplify the code flow, ESI is now zeroed and stored to memory unconditionally in shared code, so that the NULL-ness of that variable can still be used later to determine which mixed mode boot protocol is in use.
With ESI pointing to the base of the image, it can serve as a struct boot_params pointer for startup_32(), which only accesses the init_data and kernel_alignment fields (and the scratch field as a temporary stack). Zeroing ESI means that those accesses produce garbage now, even though things appear to work if the first page of memory happens to be zeroed, and the region right before LOAD_PHYSICAL_ADDR (== 16 MiB) happens to be free.
The solution is to pass a special, temporary struct boot_params to startup_32() via ESI, one that is sufficient for getting it to create the page tables correctly and is discarded right after. This involves setting a minimal alignment of 4k, only to get the statically allocated page tables line up correctly, and setting init_size to the executable image size (_end - startup_32). This ensures that the page tables are covered by the static footprint of the PE image.
Given that EFI boot no longer calls the decompressor and no longer pads the image to permit the decompressor to execute in place, the same temporary struct boot_params should be used in the EFI handover protocol based mixed mode implementation as well, to prevent the page tables from being placed outside of allocated memory.
Fixes: e2ab9eab324c ("x86/boot/compressed: Move 32-bit entrypoint code into .text section") Cc: stable@kernel.org # v6.1+ Closes: https://lore.kernel.org/all/20240321150510.GI8211@craftyguy.net/ Reported-by: Clayton Craft clayton@craftyguy.net Tested-by: Clayton Craft clayton@craftyguy.net Tested-by: Hans de Goede hdegoede@redhat.com Signed-off-by: Ard Biesheuvel ardb@kernel.org Signed-off-by: Greg Kroah-Hartman gregkh@linuxfoundation.org --- arch/x86/boot/compressed/efi_mixed.S | 20 +++++++++++++++----- 1 file changed, 15 insertions(+), 5 deletions(-)
--- a/arch/x86/boot/compressed/efi_mixed.S +++ b/arch/x86/boot/compressed/efi_mixed.S @@ -15,10 +15,12 @@ */
#include <linux/linkage.h> +#include <asm/asm-offsets.h> #include <asm/msr.h> #include <asm/page_types.h> #include <asm/processor-flags.h> #include <asm/segment.h> +#include <asm/setup.h>
.code64 .text @@ -149,6 +151,7 @@ SYM_FUNC_END(__efi64_thunk) SYM_FUNC_START(efi32_stub_entry) call 1f 1: popl %ecx + leal (efi32_boot_args - 1b)(%ecx), %ebx
/* Clear BSS */ xorl %eax, %eax @@ -163,6 +166,7 @@ SYM_FUNC_START(efi32_stub_entry) popl %ecx popl %edx popl %esi + movl %esi, 8(%ebx) jmp efi32_entry SYM_FUNC_END(efi32_stub_entry) #endif @@ -239,8 +243,6 @@ SYM_FUNC_END(efi_enter32) * * Arguments: %ecx image handle * %edx EFI system table pointer - * %esi struct bootparams pointer (or NULL when not using - * the EFI handover protocol) * * Since this is the point of no return for ordinary execution, no registers * are considered live except for the function parameters. [Note that the EFI @@ -266,9 +268,18 @@ SYM_FUNC_START_LOCAL(efi32_entry) leal (efi32_boot_args - 1b)(%ebx), %ebx movl %ecx, 0(%ebx) movl %edx, 4(%ebx) - movl %esi, 8(%ebx) movb $0x0, 12(%ebx) // efi_is64
+ /* + * Allocate some memory for a temporary struct boot_params, which only + * needs the minimal pieces that startup_32() relies on. + */ + subl $PARAM_SIZE, %esp + movl %esp, %esi + movl $PAGE_SIZE, BP_kernel_alignment(%esi) + movl $_end - 1b, BP_init_size(%esi) + subl $startup_32 - 1b, BP_init_size(%esi) + /* Disable paging */ movl %cr0, %eax btrl $X86_CR0_PG_BIT, %eax @@ -294,8 +305,7 @@ SYM_FUNC_START(efi32_pe_entry)
movl 8(%ebp), %ecx // image_handle movl 12(%ebp), %edx // sys_table - xorl %esi, %esi - jmp efi32_entry // pass %ecx, %edx, %esi + jmp efi32_entry // pass %ecx, %edx // no other registers remain live
2: popl %edi // restore callee-save registers