[PATCH 6.12 111/567] x86/fpu: Fix FPU state core dump truncation on CPUs with no extended xfeatures

Greg Kroah-Hartman
2026-01-06T17:20:20Z

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

[ Upstream commit c8161e5304abb26e6c0bec6efc947992500fa6c5 ]

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.

Fixes: ba386777a30b ("x86/elf: Add a new FPU buffer layout info to x86 core files")
Signed-off-by: Yongxin Liu <yongxin.liu@windriver.com>
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Link: https://patch.msgid.link/20251210000219.4094353-2-yongxin.liu@windriver.com
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
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 22abb5ee0cf2..aacb59c4a35c 100644
--- a/arch/x86/kernel/fpu/xstate.c
+++ b/arch/x86/kernel/fpu/xstate.c
@@ -1879,7 +1879,7 @@ static int dump_xsave_layout_desc(struct coredump_params *cprm)
};

if (!dump_emit(cprm, &xc, sizeof(xc)))
- return 0;
+ return -1;

num_records++;
}
@@ -1917,7 +1917,7 @@ 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 */
--
2.51.0