[PATCH] Remove all register pops before sysexit
This patch, which depends on the previous %ebx -> %ebp patch, removes all pop instruction in the sysenter return path. This leaks the thread_info address to user mode but this shouldn't be a security problem. This is what happens to the various registers: %eax: return value from system call: already in place %ebx, %esi, %edi: saved by the C compiler %ecx, %edx, %ebp: restored by user mode, fixed values by kernels %esp, eip: copied to %ecx/%edx and restored by sysexit %ds, %es: initialized to __USER_DS on kernel entry %cs, %ss: restored by sysexit based on msr %fs, %gs: not modified by the kernel (saved around context switch) eflags: not preserved, iopl saved around context switch FP, XMM: any code that modifies them must save/restore them Note that while it is possible to change %ebx, %esi, %edi, %ecx, %edx or %ebp via struct pt_regs, anything that does should set TIF_IRET or another work flag (and it hopefully already does).
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