From: Andy Lutomirski luto@kernel.org
commit 4c4fd55d3d59a41ddfa6ecba7e76928921759f43 upstream.
When re-building the IRET frame we use %eax as an destination %esp, make sure to then also match the segment for when there is a nonzero SS base (ESPFIX).
[peterz: Changelog and minor edits] Fixes: 3c88c692c287 ("x86/stackframe/32: Provide consistent pt_regs") Signed-off-by: Andy Lutomirski luto@kernel.org Signed-off-by: Peter Zijlstra (Intel) peterz@infradead.org Cc: stable@kernel.org Signed-off-by: Greg Kroah-Hartman gregkh@linuxfoundation.org
--- arch/x86/entry/entry_32.S | 19 ++++++++++++++----- 1 file changed, 14 insertions(+), 5 deletions(-)
--- a/arch/x86/entry/entry_32.S +++ b/arch/x86/entry/entry_32.S @@ -210,6 +210,8 @@ /* * The high bits of the CS dword (__csh) are used for CS_FROM_*. * Clear them in case hardware didn't do this for us. + * + * Be careful: we may have nonzero SS base due to ESPFIX. */ andl $0x0000ffff, 3*4(%esp)
@@ -263,6 +265,13 @@ .endm
.macro IRET_FRAME + /* + * We're called with %ds, %es, %fs, and %gs from the interrupted + * frame, so we shouldn't use them. Also, we may be in ESPFIX + * mode and therefore have a nonzero SS base and an offset ESP, + * so any attempt to access the stack needs to use SS. (except for + * accesses through %esp, which automatically use SS.) + */ testl $CS_FROM_KERNEL, 1*4(%esp) jz .Lfinished_frame_@
@@ -276,20 +285,20 @@ movl 5*4(%esp), %eax # (modified) regs->sp
movl 4*4(%esp), %ecx # flags - movl %ecx, -4(%eax) + movl %ecx, %ss:-1*4(%eax)
movl 3*4(%esp), %ecx # cs andl $0x0000ffff, %ecx - movl %ecx, -8(%eax) + movl %ecx, %ss:-2*4(%eax)
movl 2*4(%esp), %ecx # ip - movl %ecx, -12(%eax) + movl %ecx, %ss:-3*4(%eax)
movl 1*4(%esp), %ecx # eax - movl %ecx, -16(%eax) + movl %ecx, %ss:-4*4(%eax)
popl %ecx - lea -16(%eax), %esp + lea -4*4(%eax), %esp popl %eax .Lfinished_frame_@: .endm