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-rw-r--r--tools/testing/selftests/x86/sigreturn.c46
1 files changed, 29 insertions, 17 deletions
diff --git a/tools/testing/selftests/x86/sigreturn.c b/tools/testing/selftests/x86/sigreturn.c
index 246145b84a12..2559e2c01793 100644
--- a/tools/testing/selftests/x86/sigreturn.c
+++ b/tools/testing/selftests/x86/sigreturn.c
@@ -612,19 +612,38 @@ static int test_valid_sigreturn(int cs_bits, bool use_16bit_ss, int force_ss)
greg_t req = requested_regs[i], res = resulting_regs[i];
if (i == REG_TRAPNO || i == REG_IP)
continue; /* don't care */
- if (i == REG_SP) {
- printf("\tSP: %llx -> %llx\n", (unsigned long long)req,
- (unsigned long long)res);
+ if (i == REG_SP) {
/*
- * In many circumstances, the high 32 bits of rsp
- * are zeroed. For example, we could be a real
- * 32-bit program, or we could hit any of a number
- * of poorly-documented IRET or segmented ESP
- * oddities. If this happens, it's okay.
+ * If we were using a 16-bit stack segment, then
+ * the kernel is a bit stuck: IRET only restores
+ * the low 16 bits of ESP/RSP if SS is 16-bit.
+ * The kernel uses a hack to restore bits 31:16,
+ * but that hack doesn't help with bits 63:32.
+ * On Intel CPUs, bits 63:32 end up zeroed, and, on
+ * AMD CPUs, they leak the high bits of the kernel
+ * espfix64 stack pointer. There's very little that
+ * the kernel can do about it.
+ *
+ * Similarly, if we are returning to a 32-bit context,
+ * the CPU will often lose the high 32 bits of RSP.
*/
- if (res == (req & 0xFFFFFFFF))
- continue; /* OK; not expected to work */
+
+ if (res == req)
+ continue;
+
+ if (cs_bits != 64 && ((res ^ req) & 0xFFFFFFFF) == 0) {
+ printf("[NOTE]\tSP: %llx -> %llx\n",
+ (unsigned long long)req,
+ (unsigned long long)res);
+ continue;
+ }
+
+ printf("[FAIL]\tSP mismatch: requested 0x%llx; got 0x%llx\n",
+ (unsigned long long)requested_regs[i],
+ (unsigned long long)resulting_regs[i]);
+ nerrs++;
+ continue;
}
bool ignore_reg = false;
@@ -663,13 +682,6 @@ static int test_valid_sigreturn(int cs_bits, bool use_16bit_ss, int force_ss)
}
if (requested_regs[i] != resulting_regs[i] && !ignore_reg) {
- /*
- * SP is particularly interesting here. The
- * usual cause of failures is that we hit the
- * nasty IRET case of returning to a 16-bit SS,
- * in which case bits 16:31 of the *kernel*
- * stack pointer persist in ESP.
- */
printf("[FAIL]\tReg %d mismatch: requested 0x%llx; got 0x%llx\n",
i, (unsigned long long)requested_regs[i],
(unsigned long long)resulting_regs[i]);