linux-kernel - [PATCH v2] x86/elf: Fix core dump truncation on CPUs with no extended xfeatures

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Message-ID: <20251210000219.4094353-2-yongxin.liu@windriver.com>
Date: Wed, 10 Dec 2025 08:02:20 +0800
From: yongxin.liu@...driver.com
To: x86@...nel.org
Cc: linux-kernel@...r.kernel.org, bp@...en8.de, tglx@...utronix.de,
        mingo@...hat.com, dave.hansen@...ux.intel.com, vigbalas@....com,
        stable@...r.kernel.org
Subject: [PATCH v2] x86/elf: Fix core dump truncation on CPUs with no extended xfeatures

From: Yongxin Liu <yongxin.liu@...driver.com>

Zero can be a valid value of num_records. For example, on Intel Atom x6425RE,
only x87 and SSE are supported (features 0, 1), and fpu_user_cfg.max_features
is 3. The for_each_extended_xfeature() loop only iterates feature 2, which is
not enabled, so num_records = 0. This is valid and should not cause core dump
failure.

The issue is that dump_xsave_layout_desc() returns 0 for both genuine errors
(dump_emit() failure) and valid cases (no extended features). Use negative
return values for errors and only abort on genuine failures.

Cc: stable@...r.kernel.org
Fixes: ba386777a30b ("x86/elf: Add a new FPU buffer layout info to x86 core files")
Signed-off-by: Yongxin Liu <yongxin.liu@...driver.com>
---
V2: Keep error checking but use negative value for genuine error
V1: Remove error checking entirely
---
 arch/x86/kernel/fpu/xstate.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/arch/x86/kernel/fpu/xstate.c b/arch/x86/kernel/fpu/xstate.c
index 48113c5193aa..76153dfb58c9 100644
--- a/arch/x86/kernel/fpu/xstate.c
+++ b/arch/x86/kernel/fpu/xstate.c
@@ -1946,7 +1946,7 @@ static int dump_xsave_layout_desc(struct coredump_params *cprm)
 		};
 
 		if (!dump_emit(cprm, &xc, sizeof(xc)))
-			return 0;
+			return -1;
 
 		num_records++;
 	}
@@ -1984,7 +1984,7 @@ int elf_coredump_extra_notes_write(struct coredump_params *cprm)
 		return 1;
 
 	num_records = dump_xsave_layout_desc(cprm);
-	if (!num_records)
+	if (num_records < 0)
 		return 1;
 
 	/* Total size should be equal to the number of records */
-- 
2.46.2