efi/x86: Decompress at start of PE image load address

When booted via PE loader, define image_offset to hold the offset of
startup_32() from the start of the PE image, and use it as the start of
the decompression buffer.

[ mingo: Fixed the grammar in the comments. ]

Signed-off-by: Arvind Sankar <nivedita@alum.mit.edu>
Signed-off-by: Ard Biesheuvel <ardb@kernel.org>
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Link: https://lore.kernel.org/r/20200303221205.4048668-3-nivedita@alum.mit.edu
Link: https://lore.kernel.org/r/20200308080859.21568-17-ardb@kernel.org

diff --git a/arch/x86/boot/compressed/head_32.S b/arch/x86/boot/compressed/head_32.S
index 8941825..ab33070 100644 (file)
--- a/arch/x86/boot/compressed/head_32.S
+++ b/arch/x86/boot/compressed/head_32.S
@@ -100,6 +100,19 @@ SYM_FUNC_START(startup_32)
 
 #ifdef CONFIG_RELOCATABLE
        movl    %edx, %ebx
+
+#ifdef CONFIG_EFI_STUB
+/*
+ * If we were loaded via the EFI LoadImage service, startup_32() will be at an
+ * offset to the start of the space allocated for the image. efi_pe_entry() will
+ * set up image_offset to tell us where the image actually starts, so that we
+ * can use the full available buffer.
+ *     image_offset = startup_32 - image_base
+ * Otherwise image_offset will be zero and has no effect on the calculations.
+ */
+       subl    image_offset(%edx), %ebx
+#endif
+
        movl    BP_kernel_alignment(%esi), %eax
        decl    %eax
        addl    %eax, %ebx
@@ -226,6 +239,10 @@ SYM_DATA_START_LOCAL(gdt)
        .quad   0x00cf92000000ffff      /* __KERNEL_DS */
 SYM_DATA_END_LABEL(gdt, SYM_L_LOCAL, gdt_end)
 
+#ifdef CONFIG_EFI_STUB
+SYM_DATA(image_offset, .long 0)
+#endif
+
 /*
  * Stack and heap for uncompression
  */

diff --git a/arch/x86/boot/compressed/head_64.S b/arch/x86/boot/compressed/head_64.S
index 5d8338a..d4657d3 100644 (file)
--- a/arch/x86/boot/compressed/head_64.S
+++ b/arch/x86/boot/compressed/head_64.S
@@ -99,6 +99,19 @@ SYM_FUNC_START(startup_32)
 
 #ifdef CONFIG_RELOCATABLE
        movl    %ebp, %ebx
+
+#ifdef CONFIG_EFI_STUB
+/*
+ * If we were loaded via the EFI LoadImage service, startup_32 will be at an
+ * offset to the start of the space allocated for the image. efi_pe_entry will
+ * set up image_offset to tell us where the image actually starts, so that we
+ * can use the full available buffer.
+ *     image_offset = startup_32 - image_base
+ * Otherwise image_offset will be zero and has no effect on the calculations.
+ */
+       subl    image_offset(%ebp), %ebx
+#endif
+
        movl    BP_kernel_alignment(%esi), %eax
        decl    %eax
        addl    %eax, %ebx
@@ -111,9 +124,8 @@ SYM_FUNC_START(startup_32)
 1:
 
        /* Target address to relocate to for decompression */
-       movl    BP_init_size(%esi), %eax
-       subl    $_end, %eax
-       addl    %eax, %ebx
+       addl    BP_init_size(%esi), %ebx
+       subl    $_end, %ebx
 
 /*
  * Prepare for entering 64 bit mode
@@ -299,6 +311,20 @@ SYM_CODE_START(startup_64)
        /* Start with the delta to where the kernel will run at. */
 #ifdef CONFIG_RELOCATABLE
        leaq    startup_32(%rip) /* - $startup_32 */, %rbp
+
+#ifdef CONFIG_EFI_STUB
+/*
+ * If we were loaded via the EFI LoadImage service, startup_32 will be at an
+ * offset to the start of the space allocated for the image. efi_pe_entry will
+ * set up image_offset to tell us where the image actually starts, so that we
+ * can use the full available buffer.
+ *     image_offset = startup_32 - image_base
+ * Otherwise image_offset will be zero and has no effect on the calculations.
+ */
+       movl    image_offset(%rip), %eax
+       subq    %rax, %rbp
+#endif
+
        movl    BP_kernel_alignment(%rsi), %eax
        decl    %eax
        addq    %rax, %rbp
@@ -647,6 +673,10 @@ SYM_DATA_START_LOCAL(gdt)
        .quad   0x0000000000000000      /* TS continued */
 SYM_DATA_END_LABEL(gdt, SYM_L_LOCAL, gdt_end)
 
+#ifdef CONFIG_EFI_STUB
+SYM_DATA(image_offset, .long 0)
+#endif
+
 #ifdef CONFIG_EFI_MIXED
 SYM_DATA_LOCAL(efi32_boot_args, .long 0, 0, 0)
 SYM_DATA(efi_is64, .byte 1)
@@ -712,6 +742,12 @@ SYM_FUNC_START(efi32_pe_entry)
        movl    -4(%ebp), %esi                  // loaded_image
        movl    LI32_image_base(%esi), %esi     // loaded_image->image_base
        movl    %ebx, %ebp                      // startup_32 for efi32_pe_stub_entry
+       /*
+        * We need to set the image_offset variable here since startup_32() will
+        * use it before we get to the 64-bit efi_pe_entry() in C code.
+        */
+       subl    %esi, %ebx
+       movl    %ebx, image_offset(%ebp)        // save image_offset
        jmp     efi32_pe_stub_entry
 
 2:     popl    %edi                            // restore callee-save registers

diff --git a/drivers/firmware/efi/libstub/x86-stub.c b/drivers/firmware/efi/libstub/x86-stub.c
index 69a942f..3e1bc8a 100644 (file)
--- a/drivers/firmware/efi/libstub/x86-stub.c
+++ b/drivers/firmware/efi/libstub/x86-stub.c
@@ -19,6 +19,7 @@
 
 static efi_system_table_t *sys_table;
 extern const bool efi_is64;
+extern u32 image_offset;
 
 __pure efi_system_table_t *efi_system_table(void)
 {
@@ -365,6 +366,7 @@ efi_status_t __efiapi efi_pe_entry(efi_handle_t handle,
        struct boot_params *boot_params;
        struct setup_header *hdr;
        efi_loaded_image_t *image;
+       void *image_base;
        efi_guid_t proto = LOADED_IMAGE_PROTOCOL_GUID;
        int options_size = 0;
        efi_status_t status;
@@ -385,7 +387,10 @@ efi_status_t __efiapi efi_pe_entry(efi_handle_t handle,
                efi_exit(handle, status);
        }
 
-       hdr = &((struct boot_params *)efi_table_attr(image, image_base))->hdr;
+       image_base = efi_table_attr(image, image_base);
+       image_offset = (void *)startup_32 - image_base;
+
+       hdr = &((struct boot_params *)image_base)->hdr;
        above4g = hdr->xloadflags & XLF_CAN_BE_LOADED_ABOVE_4G;
 
        status = efi_allocate_pages(0x4000, (unsigned long *)&boot_params,
@@ -400,7 +405,7 @@ efi_status_t __efiapi efi_pe_entry(efi_handle_t handle,
        hdr = &boot_params->hdr;
 
        /* Copy the second sector to boot_params */
-       memcpy(&hdr->jump, efi_table_attr(image, image_base) + 512, 512);
+       memcpy(&hdr->jump, image_base + 512, 512);
 
        /*
         * Fill out some of the header fields ourselves because the
@@ -727,7 +732,7 @@ unsigned long efi_main(efi_handle_t handle,
         * If the kernel isn't already loaded at the preferred load
         * address, relocate it.
         */
-       if (bzimage_addr != hdr->pref_address) {
+       if (bzimage_addr - image_offset != hdr->pref_address) {
                status = efi_relocate_kernel(&bzimage_addr,
                                             hdr->init_size, hdr->init_size,
                                             hdr->pref_address,
@@ -737,6 +742,12 @@ unsigned long efi_main(efi_handle_t handle,
                        efi_printk("efi_relocate_kernel() failed!\n");
                        goto fail;
                }
+               /*
+                * Now that we've copied the kernel elsewhere, we no longer
+                * have a set up block before startup_32(), so reset image_offset
+                * to zero in case it was set earlier.
+                */
+               image_offset = 0;
        }
 
        /*