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cfi: add __cficanonical

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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@google.com>
Reviewed-by: Kees Cook <keescook@chromium.org>
Acked-by: Bjorn Helgaas <bhelgaas@google.com>   # pci.h
Tested-by: Nathan Chancellor <nathan@kernel.org>
Signed-off-by: Kees Cook <keescook@chromium.org>
Link: https://lore.kernel.org/r/20210408182843.1754385-3-samitolvanen@google.com
This commit is contained in:
Sami Tolvanen 2021-04-08 11:28:27 -07:00 committed by Kees Cook
parent cf68fffb66
commit ff301ceb52
4 changed files with 9 additions and 4 deletions
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1
include/linux/compiler-clang.h
View file

@ -63,3 +63,4 @@
#endif
#define __nocfi __attribute__((__no_sanitize__("cfi")))
#define __cficanonical __attribute__((__cfi_canonical_jump_table__))

4
include/linux/compiler_types.h
View file

@ -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

4
include/linux/init.h
View file

@ -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(); \
} \

4
include/linux/pci.h
View file

@ -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); \
} \