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Date: Thu, 1 Apr 2021 16:32:00 -0700 From: Sami Tolvanen <samitolvanen@...gle.com> To: Kees Cook <keescook@...omium.org> Cc: Nathan Chancellor <nathan@...nel.org>, Nick Desaulniers <ndesaulniers@...gle.com>, Masahiro Yamada <masahiroy@...nel.org>, Will Deacon <will@...nel.org>, Jessica Yu <jeyu@...nel.org>, Arnd Bergmann <arnd@...db.de>, Tejun Heo <tj@...nel.org>, "Paul E. McKenney" <paulmck@...nel.org>, Christoph Hellwig <hch@...radead.org>, Peter Zijlstra <peterz@...radead.org>, Sedat Dilek <sedat.dilek@...il.com>, Mark Rutland <mark.rutland@....com>, Catalin Marinas <catalin.marinas@....com>, bpf@...r.kernel.org, linux-hardening@...r.kernel.org, linux-arch@...r.kernel.org, linux-arm-kernel@...ts.infradead.org, linux-kbuild@...r.kernel.org, linux-pci@...r.kernel.org, linux-kernel@...r.kernel.org, clang-built-linux@...glegroups.com, Sami Tolvanen <samitolvanen@...gle.com> Subject: [PATCH v5 02/18] 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: <noncanonical.cfi_jt>: /* In C, &noncanonical points here */ jmp noncanonical ... <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 <function>.cfi and points the original symbol to the jump table entry instead: <canonical>: /* jump table entry */ jmp canonical.cfi ... <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 <samitolvanen@...gle.com> Reviewed-by: Kees Cook <keescook@...omium.org> Acked-by: Bjorn Helgaas <bhelgaas@...gle.com> # pci.h --- 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 6de9d0c9377e..adbe76b203e2 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 796935a37e37..d29bda7f6ebd 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 b3ea15348fbd..045ad1650ed1 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 86c799c97b77..39684b72db91 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); \ } \ -- 2.31.0.208.g409f899ff0-goog
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