From: Kees Cook keescook@chromium.org
[ Upstream commit f387e86d3a74407bdd9c5815820ac9d060962840 ]
To be sufficiently out of range for the usercopy test to see the lifetime mismatch, expand the size of the "bad" buffer, which will let it be beyond current_stack_pointer regardless of stack growth direction. Paired with the recent addition of stack depth checking under CONFIG_HARDENED_USERCOPY=y, this will correctly start tripping again.
Reported-by: Muhammad Usama Anjum usama.anjum@collabora.com Cc: Arnd Bergmann arnd@arndb.de Cc: Greg Kroah-Hartman gregkh@linuxfoundation.org Reviewed-by: Muhammad Usama Anjum usama.anjum@collabora.com Link: https://lore.kernel.org/lkml/762faf1b-0443-5ddf-4430-44a20cf2ec4d@collabora.... Signed-off-by: Kees Cook keescook@chromium.org Signed-off-by: Sasha Levin sashal@kernel.org --- drivers/misc/lkdtm/usercopy.c | 17 ++++++++++++++--- 1 file changed, 14 insertions(+), 3 deletions(-)
diff --git a/drivers/misc/lkdtm/usercopy.c b/drivers/misc/lkdtm/usercopy.c index e172719dd86d..4617c63b1026 100644 --- a/drivers/misc/lkdtm/usercopy.c +++ b/drivers/misc/lkdtm/usercopy.c @@ -30,12 +30,12 @@ static const unsigned char test_text[] = "This is a test.\n"; */ static noinline unsigned char *trick_compiler(unsigned char *stack) { - return stack + 0; + return stack + unconst; }
static noinline unsigned char *do_usercopy_stack_callee(int value) { - unsigned char buf[32]; + unsigned char buf[128]; int i;
/* Exercise stack to avoid everything living in registers. */ @@ -43,7 +43,12 @@ static noinline unsigned char *do_usercopy_stack_callee(int value) buf[i] = value & 0xff; }
- return trick_compiler(buf); + /* + * Put the target buffer in the middle of stack allocation + * so that we don't step on future stack users regardless + * of stack growth direction. + */ + return trick_compiler(&buf[(128/2)-32]); }
static noinline void do_usercopy_stack(bool to_user, bool bad_frame) @@ -66,6 +71,12 @@ static noinline void do_usercopy_stack(bool to_user, bool bad_frame) bad_stack -= sizeof(unsigned long); }
+#ifdef ARCH_HAS_CURRENT_STACK_POINTER + pr_info("stack : %px\n", (void *)current_stack_pointer); +#endif + pr_info("good_stack: %px-%px\n", good_stack, good_stack + sizeof(good_stack)); + pr_info("bad_stack : %px-%px\n", bad_stack, bad_stack + sizeof(good_stack)); + user_addr = vm_mmap(NULL, 0, PAGE_SIZE, PROT_READ | PROT_WRITE | PROT_EXEC, MAP_ANONYMOUS | MAP_PRIVATE, 0);