[PATCH 5/8] efi/x86: Allocate only the required 32 bytes for the GDT
From: Arvind Sankar <hidden>
Date: 2020-01-30 20:04:49
Also in:
linux-efi
Subsystem:
the rest, x86 architecture (32-bit and 64-bit) · Maintainers:
Linus Torvalds, Thomas Gleixner, Ingo Molnar, Borislav Petkov, Dave Hansen
For the 32-bit boot GDT, we only need 4 descriptors. Allocate the required 32 bytes using allocate_pool, rather than always allocating a full page. The UEFI spec guarantees that allocate_pool returns an 8-byte aligned buffer, so we don't need to do additional alignment. The "size" stored in the GDT pointer should be one less than the true size of the GDT. Signed-off-by: Arvind Sankar <redacted> --- arch/x86/boot/compressed/eboot.c | 13 +++++++++++-- 1 file changed, 11 insertions(+), 2 deletions(-)
diff --git a/arch/x86/boot/compressed/eboot.c b/arch/x86/boot/compressed/eboot.c
index a72cfda91d7e..2447e4508aa4 100644
--- a/arch/x86/boot/compressed/eboot.c
+++ b/arch/x86/boot/compressed/eboot.c@@ -350,14 +350,23 @@ static efi_status_t setup_gdt(struct desc_ptr *gdt) efi_status_t status; struct desc_struct *desc; - gdt->size = 0x800; - status = efi_low_alloc(gdt->size, 8, (unsigned long *)&gdt->address); + gdt->size = 0x20; + status = efi_bs_call(allocate_pool, EFI_LOADER_DATA, gdt->size, + (void **)&gdt->address); if (status != EFI_SUCCESS) { efi_printk("Failed to allocate memory for 'gdt'\n"); return status; } memset((char *)gdt->address, 0x0, gdt->size); + + /* + * The "size" stored in the GDT pointer is actually a limit value, + * which when added to the base address gives the address of the last + * byte of the GDT. Hence it should be one less than the true size. + */ + gdt->size--; + desc = (struct desc_struct *)gdt->address; /* The first GDT is a dummy. */
--
2.24.1