The compacted-format XSAVES area is determined at boot time and
never changed after. The field xsave.header.xcomp_bv indicates
which components are in the fixed XSAVES format.
In fpstate_init() we did not set xcomp_bv to reflect the XSAVES
format since at the time there is no valid data.
However, after we do copy_init_fpstate_to_fpregs() in fpu__clear(),
as in commit: b22cbe404a9cc3c7949e380fa1861e31934c8978, and when
__fpu_restore_sig() does fpu__restore() for a COMPAT-mode app,
a #GP occurs. This can be easily triggered by doing valgrind on
a COMPAT-mode "Hello World," as reported by Joakim Tjernlund and
others:
https://bugzilla.kernel.org/show_bug.cgi?id=190061
Fix it by setting xcomp_bv correctly.
Signed-off-by: Yu-cheng Yu <[email protected]>
Reported-by: Joakim Tjernlund <[email protected]>
---
arch/x86/kernel/fpu/core.c | 4 +++-
1 file changed, 3 insertions(+), 1 deletion(-)
diff --git a/arch/x86/kernel/fpu/core.c b/arch/x86/kernel/fpu/core.c
index c289e2f..e540dc1 100644
--- a/arch/x86/kernel/fpu/core.c
+++ b/arch/x86/kernel/fpu/core.c
@@ -9,6 +9,7 @@
#include <asm/fpu/regset.h>
#include <asm/fpu/signal.h>
#include <asm/fpu/types.h>
+#include <asm/fpu/xstate.h>
#include <asm/traps.h>
#include <linux/hardirq.h>
@@ -235,7 +236,8 @@ void fpstate_init(union fpregs_state *state)
* it will #GP. Make sure it is replaced after the memset().
*/
if (static_cpu_has(X86_FEATURE_XSAVES))
- state->xsave.header.xcomp_bv = XCOMP_BV_COMPACTED_FORMAT;
+ state->xsave.header.xcomp_bv = XCOMP_BV_COMPACTED_FORMAT |
+ xfeatures_mask;
if (static_cpu_has(X86_FEATURE_FXSR))
fpstate_init_fxstate(&state->fxsave);
--
1.9.1
