From ff301ceb5299551c3650d0e07ba879b766da4cc0 Mon Sep 17 00:00:00 2001 From: Sami Tolvanen Date: Thu, 8 Apr 2021 11:28:27 -0700 Subject: [PATCH] cfi: add __cficanonical With CONFIG_CFI_CLANG, the compiler replaces a function address taken in C code with the address of a local jump table entry, which passes runtime indirect call checks. However, the compiler won't replace addresses taken in assembly code, which will result in a CFI failure if we later jump to such an address in instrumented C code. The code generated for the non-canonical jump table looks this: : /* In C, &noncanonical points here */ jmp noncanonical ... : /* function body */ ... This change adds the __cficanonical attribute, which tells the compiler to use a canonical jump table for the function instead. This means the compiler will rename the actual function to .cfi and points the original symbol to the jump table entry instead: : /* jump table entry */ jmp canonical.cfi ... : /* function body */ ... As a result, the address taken in assembly, or other non-instrumented code always points to the jump table and therefore, can be used for indirect calls in instrumented code without tripping CFI checks. Signed-off-by: Sami Tolvanen Reviewed-by: Kees Cook Acked-by: Bjorn Helgaas # pci.h Tested-by: Nathan Chancellor Signed-off-by: Kees Cook Link: https://lore.kernel.org/r/20210408182843.1754385-3-samitolvanen@google.com --- include/linux/compiler-clang.h | 1 + include/linux/compiler_types.h | 4 ++++ include/linux/init.h | 4 ++-- include/linux/pci.h | 4 ++-- 4 files changed, 9 insertions(+), 4 deletions(-) diff --git a/include/linux/compiler-clang.h b/include/linux/compiler-clang.h index 6de9d0c9377e9..adbe76b203e2f 100644 --- a/include/linux/compiler-clang.h +++ b/include/linux/compiler-clang.h @@ -63,3 +63,4 @@ #endif #define __nocfi __attribute__((__no_sanitize__("cfi"))) +#define __cficanonical __attribute__((__cfi_canonical_jump_table__)) diff --git a/include/linux/compiler_types.h b/include/linux/compiler_types.h index 796935a37e373..d29bda7f6ebdd 100644 --- a/include/linux/compiler_types.h +++ b/include/linux/compiler_types.h @@ -246,6 +246,10 @@ struct ftrace_likely_data { # define __nocfi #endif +#ifndef __cficanonical +# define __cficanonical +#endif + #ifndef asm_volatile_goto #define asm_volatile_goto(x...) asm goto(x) #endif diff --git a/include/linux/init.h b/include/linux/init.h index b3ea15348fbdc..045ad1650ed16 100644 --- a/include/linux/init.h +++ b/include/linux/init.h @@ -220,8 +220,8 @@ extern bool initcall_debug; __initcall_name(initstub, __iid, id) #define __define_initcall_stub(__stub, fn) \ - int __init __stub(void); \ - int __init __stub(void) \ + int __init __cficanonical __stub(void); \ + int __init __cficanonical __stub(void) \ { \ return fn(); \ } \ diff --git a/include/linux/pci.h b/include/linux/pci.h index 86c799c97b779..39684b72db915 100644 --- a/include/linux/pci.h +++ b/include/linux/pci.h @@ -1944,8 +1944,8 @@ enum pci_fixup_pass { #ifdef CONFIG_LTO_CLANG #define __DECLARE_PCI_FIXUP_SECTION(sec, name, vendor, device, class, \ class_shift, hook, stub) \ - void stub(struct pci_dev *dev); \ - void stub(struct pci_dev *dev) \ + void __cficanonical stub(struct pci_dev *dev); \ + void __cficanonical stub(struct pci_dev *dev) \ { \ hook(dev); \ } \ -- 2.30.2