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lkdtm: Fix CFI_BACKWARD on RISC-V

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On RISC-V, the return address is before the current frame pointer,
unlike on most other architectures. Use the correct offset on RISC-V
to fix the CFI_BACKWARD test.

Signed-off-by: Sami Tolvanen <samitolvanen@google.com>
Acked-by: Kees Cook <keescook@chromium.org>
Tested-by: Nathan Chancellor <nathan@kernel.org>
Link: https://lore.kernel.org/r/20230927224757.1154247-14-samitolvanen@google.com
Signed-off-by: Palmer Dabbelt <palmer@rivosinc.com>
This commit is contained in:
Sami Tolvanen 2023-09-27 22:48:04 +00:00 committed by Palmer Dabbelt
parent c40fef858d
commit 245561ba6d
No known key found for this signature in database
GPG key ID: 2E1319F35FBB1889
1 changed files with 11 additions and 2 deletions
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13
drivers/misc/lkdtm/cfi.c
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@ -68,12 +68,20 @@ static void lkdtm_CFI_FORWARD_PROTO(void)
#define no_pac_addr(addr) \
((__force __typeof__(addr))((uintptr_t)(addr) | PAGE_OFFSET))
#ifdef CONFIG_RISCV
/* https://github.com/riscv-non-isa/riscv-elf-psabi-doc/blob/master/riscv-cc.adoc#frame-pointer-convention */
#define FRAME_RA_OFFSET (-1)
#else
#define FRAME_RA_OFFSET 1
#endif
/* The ultimate ROP gadget. */
static noinline __no_ret_protection
void set_return_addr_unchecked(unsigned long *expected, unsigned long *addr)
{
/* Use of volatile is to make sure final write isn't seen as a dead store. */
unsigned long * volatile *ret_addr = (unsigned long **)__builtin_frame_address(0) + 1;
unsigned long * volatile *ret_addr =
(unsigned long **)__builtin_frame_address(0) + FRAME_RA_OFFSET;
/* Make sure we've found the right place on the stack before writing it. */
if (no_pac_addr(*ret_addr) == expected)
@ -88,7 +96,8 @@ static noinline
void set_return_addr(unsigned long *expected, unsigned long *addr)
{
/* Use of volatile is to make sure final write isn't seen as a dead store. */
unsigned long * volatile *ret_addr = (unsigned long **)__builtin_frame_address(0) + 1;
unsigned long * volatile *ret_addr =
(unsigned long **)__builtin_frame_address(0) + FRAME_RA_OFFSET;
/* Make sure we've found the right place on the stack before writing it. */
if (no_pac_addr(*ret_addr) == expected)