On Tue, Sep 20, 2022 at 09:27:51AM +0200, Peter Zijlstra wrote: > On Tue, Sep 20, 2022 at 02:08:55PM +0800, Guo Ren wrote: > > On Mon, Sep 19, 2022 at 9:45 PM Peter Zijlstra <peterz@xxxxxxxxxxxxx> wrote: > > > > > > On Sun, Sep 18, 2022 at 11:52:43AM -0400, guoren@xxxxxxxxxx wrote: > > > > > > > +ENTRY(call_on_stack) > > > > + /* Create a frame record to save our ra and fp */ > > > > + addi sp, sp, -RISCV_SZPTR > > > > + REG_S ra, (sp) > > > > + addi sp, sp, -RISCV_SZPTR > > > > + REG_S fp, (sp) > > > > + > > > > + /* Save sp in fp */ > > > > + move fp, sp > > > > + > > > > + /* Move to the new stack and call the function there */ > > > > + li a3, IRQ_STACK_SIZE > > > > + add sp, a1, a3 > > > > + jalr a2 > > > > + > > > > + /* > > > > + * Restore sp from prev fp, and fp, ra from the frame > > > > + */ > > > > + move sp, fp > > > > + REG_L fp, (sp) > > > > + addi sp, sp, RISCV_SZPTR > > > > + REG_L ra, (sp) > > > > + addi sp, sp, RISCV_SZPTR > > > > + ret > > > > +ENDPROC(call_on_stack) > > > > > > IIRC x86_64 moved away from a stack-switch function like this because it > > > presents a convenient exploit gadget. > > I found: > > https://lore.kernel.org/all/20210204204903.350275743@xxxxxxxxxxxxx/ > > > > - The fact that the stack switching code ended up being an easy to find > > exploit gadget. > > > > What's the exploit gadget? Do you have a ref link? Thx. > > Sadly no, I do not. Kees might. But basically it boils down to this > function taking both a stack pointer and a function pointer as > arguments (@a1 and @a2 resp. if I'm not reading this wrong). > > If an attacker can call this with arguments of its choice then it gains > full control of subsequent execution. If you inline it the hope is that the function pointers go away or at least the encompassing function doesn't have quite such a 'convenient' signature to hijack control flow.
