diff options
| author | Petr Tesarik <ptesarik@suse.com> | 2024-11-19 12:37:38 +0100 |
|---|---|---|
| committer | Andrew Morton <akpm@linux-foundation.org> | 2025-01-13 22:40:37 -0800 |
| commit | db27ad8b0209e892a9b6294aadcf9d756f41a656 (patch) | |
| tree | 6fab075f46510d9466a71dff57e15752a1f3eb67 | |
| parent | 255ff62d1586e63b6a461f0d89088d60d54d9814 (diff) | |
mm/rodata_test: use READ_ONCE() to read const variable
Patch series "Fix mm/rodata_test", v2.
Make sure that the test actually reads the read-only memory location.
Verify that the variable contains the expected value rather than any
non-zero value.
This patch (of 2):
The C compiler may optimize away the memory read of a const variable if
its value is known at compile time.
In particular, GCC14 with -O2 generates no code at all for test 1, and it
generates the following x86_64 instructions for test 3:
cmpl $195, 4(%rsp)
je .L14
That is, it replaces the read of rodata_test_data with an immediate value
and compares it to the value of the local variable "zero".
Use READ_ONCE() to undo any such compiler optimizations and enforce a
memory read.
Link: https://lkml.kernel.org/r/cover.1732016064.git.ptesarik@suse.com
Link: https://lkml.kernel.org/r/2a66dee010151b25cb143efb39091ef7530aa00a.1732016064.git.ptesarik@suse.com
Fixes: 2959a5f726f6 ("mm: add arch-independent testcases for RODATA")
Signed-off-by: Petr Tesarik <ptesarik@suse.com>
Reviewed-by: Kees Cook <kees@kernel.org>
Cc: Jinbum Park <jinb.park7@gmail.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
| -rw-r--r-- | mm/rodata_test.c | 4 |
1 files changed, 2 insertions, 2 deletions
diff --git a/mm/rodata_test.c b/mm/rodata_test.c index 6d783436951f..3b60425d80fe 100644 --- a/mm/rodata_test.c +++ b/mm/rodata_test.c @@ -20,7 +20,7 @@ void rodata_test(void) /* test 1: read the value */ /* If this test fails, some previous testrun has clobbered the state */ - if (!rodata_test_data) { + if (!READ_ONCE(rodata_test_data)) { pr_err("test 1 fails (start data)\n"); return; } @@ -33,7 +33,7 @@ void rodata_test(void) } /* test 3: check the value hasn't changed */ - if (rodata_test_data == zero) { + if (READ_ONCE(rodata_test_data) == zero) { pr_err("test data was changed\n"); return; } |