From acd644bb4abb4d9f0ba6b9ec2b356263971ef9d0 Mon Sep 17 00:00:00 2001 From: "H. Peter Anvin" Date: Wed, 30 Jan 2008 13:33:04 +0100 Subject: [PATCH] x86 setup: guard the heap against invalid stack setups If we use the bootloader-provided stack pointer, we might end up in a situation where the bootloader (incorrectly) pointed the stack in the middle of our heap. Catch this by simply comparing the computed heap end value to the stack pointer minus the defined stack size. Signed-off-by: H. Peter Anvin Signed-off-by: Ingo Molnar Signed-off-by: Thomas Gleixner --- arch/x86/boot/main.c | 24 ++++++++++++++++++------ 1 file changed, 18 insertions(+), 6 deletions(-) diff --git a/arch/x86/boot/main.c b/arch/x86/boot/main.c index 22ca62b..7828da5 100644 --- a/arch/x86/boot/main.c +++ b/arch/x86/boot/main.c @@ -100,20 +100,32 @@ static void set_bios_mode(void) #endif } -void main(void) +static void init_heap(void) { - /* First, copy the boot header into the "zeropage" */ - copy_boot_params(); + char *stack_end; - /* End of heap check */ if (boot_params.hdr.loadflags & CAN_USE_HEAP) { - heap_end = (char *)(boot_params.hdr.heap_end_ptr - +0x200-STACK_SIZE); + asm("leal %P1(%%esp),%0" + : "=r" (stack_end) : "i" (-STACK_SIZE)); + + heap_end = (char *) + ((size_t)boot_params.hdr.heap_end_ptr + 0x200); + if (heap_end > stack_end) + heap_end = stack_end; } else { /* Boot protocol 2.00 only, no heap available */ puts("WARNING: Ancient bootloader, some functionality " "may be limited!\n"); } +} + +void main(void) +{ + /* First, copy the boot header into the "zeropage" */ + copy_boot_params(); + + /* End of heap check */ + init_heap(); /* Make sure we have all the proper CPU support */ if (validate_cpu()) { -- 2.7.4