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author | H. Peter Anvin <hpa@zytor.com> | 2007-10-25 16:11:33 -0700 |
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committer | H. Peter Anvin <hpa@zytor.com> | 2007-10-25 19:55:03 -0700 |
commit | 6b6815c6d5d1dc209701d1661a7a0e09a295db2f (patch) | |
tree | 9e1c07acbc4926279fcef068efb60141c6eed2af /arch/x86/boot/header.S | |
parent | c9927c2bf4f45bb85e8b502ab3fb79ad6483c244 (diff) | |
download | linux-stable-6b6815c6d5d1dc209701d1661a7a0e09a295db2f.tar.gz linux-stable-6b6815c6d5d1dc209701d1661a7a0e09a295db2f.tar.bz2 linux-stable-6b6815c6d5d1dc209701d1661a7a0e09a295db2f.zip |
x86 setup: handle boot loaders which set up the stack incorrectly
Apparently some specific versions of LILO enter the kernel with a
stack pointer that doesn't match the rest of the segments. Make our
best attempt at untangling the resulting mess.
Signed-off-by: H. Peter Anvin <hpa@zytor.com>
Diffstat (limited to 'arch/x86/boot/header.S')
-rw-r--r-- | arch/x86/boot/header.S | 62 |
1 files changed, 44 insertions, 18 deletions
diff --git a/arch/x86/boot/header.S b/arch/x86/boot/header.S index 8353c81c41c0..6ef5a060fa11 100644 --- a/arch/x86/boot/header.S +++ b/arch/x86/boot/header.S @@ -173,7 +173,8 @@ ramdisk_size: .long 0 # its size in bytes bootsect_kludge: .long 0 # obsolete -heap_end_ptr: .word _end+1024 # (Header version 0x0201 or later) +heap_end_ptr: .word _end+STACK_SIZE-512 + # (Header version 0x0201 or later) # space from here (exclusive) down to # end of setup code can be used by setup # for local heap purposes. @@ -230,28 +231,53 @@ start_of_setup: int $0x13 #endif -# We will have entered with %cs = %ds+0x20, normalize %cs so -# it is on par with the other segments. - pushw %ds - pushw $setup2 - lretw - -setup2: # Force %es = %ds movw %ds, %ax movw %ax, %es cld -# Stack paranoia: align the stack and make sure it is good -# for both 16- and 32-bit references. In particular, if we -# were meant to have been using the full 16-bit segment, the -# caller might have set %sp to zero, which breaks %esp-based -# references. - andw $~3, %sp # dword align (might as well...) - jnz 1f - movw $0xfffc, %sp # Make sure we're not zero -1: movzwl %sp, %esp # Clear upper half of %esp - sti +# Apparently some ancient versions of LILO invoked the kernel +# with %ss != %ds, which happened to work by accident for the +# old code. If the CAN_USE_HEAP flag is set in loadflags, or +# %ss != %ds, then adjust the stack pointer. + + # Smallest possible stack we can tolerate + movw $(_end+STACK_SIZE), %cx + + movw heap_end_ptr, %dx + addw $512, %dx + jnc 1f + xorw %dx, %dx # Wraparound - whole segment available +1: testb $CAN_USE_HEAP, loadflags + jnz 2f + + # No CAN_USE_HEAP + movw %ss, %dx + cmpw %ax, %dx # %ds == %ss? + movw %sp, %dx + # If so, assume %sp is reasonably set, otherwise use + # the smallest possible stack. + jne 4f # -> Smallest possible stack... + + # Make sure the stack is at least minimum size. Take a value + # of zero to mean "full segment." +2: + andw $~3, %dx # dword align (might as well...) + jnz 3f + movw $0xfffc, %dx # Make sure we're not zero +3: cmpw %cx, %dx + jnb 5f +4: movw %cx, %dx # Minimum value we can possibly use +5: movw %ax, %ss + movzwl %dx, %esp # Clear upper half of %esp + sti # Now we should have a working stack + +# We will have entered with %cs = %ds+0x20, normalize %cs so +# it is on par with the other segments. + pushw %ds + pushw $6f + lretw +6: # Check signature at end of setup cmpl $0x5a5aaa55, setup_sig |