From e81dc127ef69887c72735a3e3868930e2bf313ed Mon Sep 17 00:00:00 2001 From: Thomas Gleixner Date: Thu, 15 Sep 2022 13:11:23 +0200 Subject: x86/callthunks: Add call patching for call depth tracking Mitigating the Intel SKL RSB underflow issue in software requires to track the call depth. That is every CALL and every RET need to be intercepted and additional code injected. The existing retbleed mitigations already include means of redirecting RET to __x86_return_thunk; this can be re-purposed and RET can be redirected to another function doing RET accounting. CALL accounting will use the function padding introduced in prior patches. For each CALL instruction, the destination symbol's padding is rewritten to do the accounting and the CALL instruction is adjusted to call into the padding. This ensures only affected CPUs pay the overhead of this accounting. Unaffected CPUs will leave the padding unused and have their 'JMP __x86_return_thunk' replaced with an actual 'RET' instruction. Objtool has been modified to supply a .call_sites section that lists all the 'CALL' instructions. Additionally the paravirt instruction sites are iterated since they will have been patched from an indirect call to direct calls (or direct instructions in which case it'll be ignored). Module handling and the actual thunk code for SKL will be added in subsequent steps. Signed-off-by: Thomas Gleixner Signed-off-by: Peter Zijlstra (Intel) Link: https://lore.kernel.org/r/20220915111147.470877038@infradead.org --- arch/x86/kernel/vmlinux.lds.S | 8 -------- 1 file changed, 8 deletions(-) (limited to 'arch/x86/kernel/vmlinux.lds.S') diff --git a/arch/x86/kernel/vmlinux.lds.S b/arch/x86/kernel/vmlinux.lds.S index b69df9e013cc..49f3f86433c7 100644 --- a/arch/x86/kernel/vmlinux.lds.S +++ b/arch/x86/kernel/vmlinux.lds.S @@ -501,11 +501,3 @@ INIT_PER_CPU(irq_stack_backing_store); #endif #endif /* CONFIG_X86_64 */ - -#ifdef CONFIG_KEXEC_CORE -#include - -. = ASSERT(kexec_control_code_size <= KEXEC_CONTROL_CODE_MAX_SIZE, - "kexec control code size is too big"); -#endif - -- cgit v1.2.3