linux-kernel - [PATCH] selftests/rseq: Fix rseq for cases without glibc support

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Message-ID: <20241210224435.15206-1-rananta@google.com>
Date: Tue, 10 Dec 2024 22:44:35 +0000
From: Raghavendra Rao Ananta <rananta@...gle.com>
To: Mathieu Desnoyers <mathieu.desnoyers@...icios.com>
Cc: Raghavendra Rao Anata <rananta@...gle.com>, linux-kernel@...r.kernel.org, kvm@...r.kernel.org, 
	linux-kselftest@...r.kernel.org, stable@...r.kernel.org
Subject: [PATCH] selftests/rseq: Fix rseq for cases without glibc support

Currently the rseq constructor, rseq_init(), assumes that glibc always
has the support for rseq symbols (__rseq_size for instance). However,
glibc supports rseq from version 2.35 onwards. As a result, for the
systems that run glibc less than 2.35, the global rseq_size remains
initialized to -1U. When a thread then tries to register for rseq,
get_rseq_min_alloc_size() would end up returning -1U, which is
incorrect. Hence, initialize rseq_size for the cases where glibc doesn't
have the support for rseq symbols.

Cc: stable@...r.kernel.org
Fixes: 73a4f5a704a2 ("selftests/rseq: Fix mm_cid test failure")
Signed-off-by: Raghavendra Rao Ananta <rananta@...gle.com>
---
 tools/testing/selftests/rseq/rseq.c | 19 +++++++++++++------
 1 file changed, 13 insertions(+), 6 deletions(-)

diff --git a/tools/testing/selftests/rseq/rseq.c b/tools/testing/selftests/rseq/rseq.c
index 5b9772cdf265..9eb5356f25fa 100644
--- a/tools/testing/selftests/rseq/rseq.c
+++ b/tools/testing/selftests/rseq/rseq.c
@@ -142,6 +142,16 @@ unsigned int get_rseq_kernel_feature_size(void)
 		return ORIG_RSEQ_FEATURE_SIZE;
 }
 
+static void set_default_rseq_size(void)
+{
+	unsigned int rseq_kernel_feature_size = get_rseq_kernel_feature_size();
+
+	if (rseq_kernel_feature_size < ORIG_RSEQ_ALLOC_SIZE)
+		rseq_size = rseq_kernel_feature_size;
+	else
+		rseq_size = ORIG_RSEQ_ALLOC_SIZE;
+}
+
 int rseq_register_current_thread(void)
 {
 	int rc;
@@ -219,12 +229,7 @@ void rseq_init(void)
 			fallthrough;
 		case ORIG_RSEQ_ALLOC_SIZE:
 		{
-			unsigned int rseq_kernel_feature_size = get_rseq_kernel_feature_size();
-
-			if (rseq_kernel_feature_size < ORIG_RSEQ_ALLOC_SIZE)
-				rseq_size = rseq_kernel_feature_size;
-			else
-				rseq_size = ORIG_RSEQ_ALLOC_SIZE;
+			set_default_rseq_size();
 			break;
 		}
 		default:
@@ -239,8 +244,10 @@ void rseq_init(void)
 		rseq_size = 0;
 		return;
 	}
+
 	rseq_offset = (void *)&__rseq_abi - rseq_thread_pointer();
 	rseq_flags = 0;
+	set_default_rseq_size();
 }
 
 static __attribute__((destructor))

base-commit: 40384c840ea1944d7c5a392e8975ed088ecf0b37
-- 
2.47.0.338.g60cca15819-goog