riscv: Enable per-task stack canaries
This enables the use of per-task stack canary values if GCC has support for emitting the stack canary reference relative to the value of tp, which holds the task struct pointer in the riscv kernel. After compare arm64 and x86 implementations, seems arm64's is more flexible and readable. The key point is how gcc get the offset of stack_canary from gs/el0_sp. x86: Use a fix offset from gs, not flexible. struct fixed_percpu_data { /* * GCC hardcodes the stack canary as %gs:40. Since the * irq_stack is the object at %gs:0, we reserve the bottom * 48 bytes of the irq stack for the canary. */ char gs_base[40]; // :( unsigned long stack_canary; }; arm64: Use -mstack-protector-guard-offset & guard-reg gcc options: -mstack-protector-guard=sysreg -mstack-protector-guard-reg=sp_el0 -mstack-protector-guard-offset=xxx riscv: Use -mstack-protector-guard-offset & guard-reg gcc options: -mstack-protector-guard=tls -mstack-protector-guard-reg=tp -mstack-protector-guard-offset=xxx GCC's implementation has been merged: commit c931e8d5a96463427040b0d11f9c4352ac22b2b0 Author: Cooper Qu <cooper.qu@linux.alibaba.com> Date: Mon Jul 13 16:15:08 2020 +0800 RISC-V: Add support for TLS stack protector canary access In the end, these codes are inserted by gcc before return: * 0xffffffe00020b396 <+120>: ld a5,1008(tp) # 0x3f0 * 0xffffffe00020b39a <+124>: xor a5,a5,a4 * 0xffffffe00020b39c <+126>: mv a0,s5 * 0xffffffe00020b39e <+128>: bnez a5,0xffffffe00020b61c <_do_fork+766> 0xffffffe00020b3a2 <+132>: ld ra,136(sp) 0xffffffe00020b3a4 <+134>: ld s0,128(sp) 0xffffffe00020b3a6 <+136>: ld s1,120(sp) 0xffffffe00020b3a8 <+138>: ld s2,112(sp) 0xffffffe00020b3aa <+140>: ld s3,104(sp) 0xffffffe00020b3ac <+142>: ld s4,96(sp) 0xffffffe00020b3ae <+144>: ld s5,88(sp) 0xffffffe00020b3b0 <+146>: ld s6,80(sp) 0xffffffe00020b3b2 <+148>: ld s7,72(sp) 0xffffffe00020b3b4 <+150>: addi sp,sp,144 0xffffffe00020b3b6 <+152>: ret ... * 0xffffffe00020b61c <+766>: auipc ra,0x7f8 * 0xffffffe00020b620 <+770>: jalr -1764(ra) # 0xffffffe000a02f38 <__stack_chk_fail> Signed-off-by: Guo Ren <guoren@linux.alibaba.com> Signed-off-by: Cooper Qu <cooper.qu@linux.alibaba.com> Reviewed-by: Kees Cook <keescook@chromium.org> Signed-off-by: Palmer Dabbelt <palmerdabbelt@google.com>
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