Commit
8ab4b00 ("[libc] Rewrite setjmp() and longjmp()") introduced a
regression in which the saved values of %ebx, %esi, and %edi were all
accidentally restored into %esp. The result is that the second and
subsequent returns from setjmp() would effectively corrupt %ebx, %esi,
%edi, and the stack pointer %esp.
Use of setjmp() and longjmp() is generally discouraged: our only use
occurs as part of the implementation of PXENV_RESTART_TFTP, since the
PXE API effectively mandates its use here. The call to setjmp()
occurs at the start of pxe_start_nbp(), where there are almost
certainly no values held in %ebx, %esi, or %edi. The corruption of
these registers therefore had no visible effect on program execution.
The corruption of %esp would have been visible on return from
pxe_start_nbp(), but there are no known PXE NBPs which first call
PXENV_RESTART_TFTP and subsequently attempt to return to the PXE base
code. The effect on program execution was therefore similar to that
of moving the stack to a pseudo-random location in the 32-bit address
space; this will often allow execution to complete successfully since
there is a high chance that the pseudo-random location will be unused.
The regression therefore went undetected for around one month.
Fix by restoring the correct registers from the saved jmp_buf
structure.
Signed-off-by: Michael Brown <mcb30@ipxe.org>
1: /* Restore stack pointer */
movl env_stack(%edx), %esp
/* Restore other registers */
- movl env_ebx(%edx), %esp
- movl env_esi(%edx), %esp
- movl env_edi(%edx), %esp
+ movl env_ebx(%edx), %ebx
+ movl env_esi(%edx), %esi
+ movl env_edi(%edx), %edi
movl env_ebp(%edx), %ebp
/* Replace return address on the new stack */
popl %ecx /* discard */