From: Arnd Bergmann <arnd@xxxxxxxx>
gcc-11 warns about using string operations on pointers that are
defined at compile time as offsets from a NULL pointer. Unfortunately
that also happens on the result of fix_to_virt(), which is a
compile-time constant for a constantn input:
arch/x86/kernel/tboot.c: In function 'tboot_probe':
arch/x86/kernel/tboot.c:70:13: error: '__builtin_memcmp_eq' specified bound 16 exceeds source size 0 [-Werror=stringop-overread]
70 | if (memcmp(&tboot_uuid, &tboot->uuid, sizeof(tboot->uuid))) {
| ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
I hope this can get addressed in gcc-11 before the release.
As a workaround, split up the tboot_probe() function in two halves
to separate the pointer generation from the usage. This is a bit
ugly, and hopefully gcc understands that the code is actually correct
before it learns to peek into the noinline function.
Link: https://gcc.gnu.org/bugzilla/show_bug.cgi?id=99578
Signed-off-by: Arnd Bergmann <arnd@xxxxxxxx>
---
arch/x86/kernel/tboot.c | 44 ++++++++++++++++++++++++-----------------
1 file changed, 26 insertions(+), 18 deletions(-)
diff --git a/arch/x86/kernel/tboot.c b/arch/x86/kernel/tboot.c
index 4c09ba110204..f9af561c3cd4 100644
--- a/arch/x86/kernel/tboot.c
+++ b/arch/x86/kernel/tboot.c
@@ -49,6 +49,30 @@ bool tboot_enabled(void)
return tboot != NULL;
}
+/* noinline to prevent gcc from warning about dereferencing constant fixaddr */
+static noinline __init bool check_tboot_version(void)
+{
+ if (memcmp(&tboot_uuid, &tboot->uuid, sizeof(tboot->uuid))) {
+ pr_warn("tboot at 0x%llx is invalid\n", boot_params.tboot_addr);
+ return false;
+ }
+
+ if (tboot->version < 5) {
+ pr_warn("tboot version is invalid: %u\n", tboot->version);
+ return false;
+ }
+
+ pr_info("found shared page at phys addr 0x%llx:\n",
+ boot_params.tboot_addr);
+ pr_debug("version: %d\n", tboot->version);
+ pr_debug("log_addr: 0x%08x\n", tboot->log_addr);
+ pr_debug("shutdown_entry: 0x%x\n", tboot->shutdown_entry);
+ pr_debug("tboot_base: 0x%08x\n", tboot->tboot_base);
+ pr_debug("tboot_size: 0x%x\n", tboot->tboot_size);
+
+ return true;
+}
+
void __init tboot_probe(void)
{
/* Look for valid page-aligned address for shared page. */
@@ -66,25 +90,9 @@ void __init tboot_probe(void)
/* Map and check for tboot UUID. */
set_fixmap(FIX_TBOOT_BASE, boot_params.tboot_addr);
- tboot = (struct tboot *)fix_to_virt(FIX_TBOOT_BASE);
- if (memcmp(&tboot_uuid, &tboot->uuid, sizeof(tboot->uuid))) {
- pr_warn("tboot at 0x%llx is invalid\n", boot_params.tboot_addr);
+ tboot = (void *)fix_to_virt(FIX_TBOOT_BASE);
+ if (!check_tboot_version())
tboot = NULL;
- return;
- }
- if (tboot->version < 5) {
- pr_warn("tboot version is invalid: %u\n", tboot->version);
- tboot = NULL;
- return;
- }
-
- pr_info("found shared page at phys addr 0x%llx:\n",
- boot_params.tboot_addr);
- pr_debug("version: %d\n", tboot->version);
- pr_debug("log_addr: 0x%08x\n", tboot->log_addr);
- pr_debug("shutdown_entry: 0x%x\n", tboot->shutdown_entry);
- pr_debug("tboot_base: 0x%08x\n", tboot->tboot_base);
- pr_debug("tboot_size: 0x%x\n", tboot->tboot_size);
}
static pgd_t *tboot_pg_dir;
--
2.29.2
