This is a note to let you know that I've just added the patch titled
x86/fpu: Stop relying on userspace for info to fault in xsave buffer
to the 6.6-stable tree which can be found at:
http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary
The filename of the patch is:
x86-fpu-stop-relying-on-userspace-for-info-to-fault-in-xsave-buffer.patch
and it can be found in the queue-6.6 subdirectory.
If you, or anyone else, feels it should not be added to the stable tree,
please let <stable@xxxxxxxxxxxxxxx> know about it.
>From d877550eaf2dc9090d782864c96939397a3c6835 Mon Sep 17 00:00:00 2001
From: Andrei Vagin <avagin@xxxxxxxxxx>
Date: Mon, 29 Jan 2024 22:36:03 -0800
Subject: x86/fpu: Stop relying on userspace for info to fault in xsave buffer
From: Andrei Vagin <avagin@xxxxxxxxxx>
commit d877550eaf2dc9090d782864c96939397a3c6835 upstream.
Before this change, the expected size of the user space buffer was
taken from fx_sw->xstate_size. fx_sw->xstate_size can be changed
from user-space, so it is possible construct a sigreturn frame where:
* fx_sw->xstate_size is smaller than the size required by valid bits in
fx_sw->xfeatures.
* user-space unmaps parts of the sigrame fpu buffer so that not all of
the buffer required by xrstor is accessible.
In this case, xrstor tries to restore and accesses the unmapped area
which results in a fault. But fault_in_readable succeeds because buf +
fx_sw->xstate_size is within the still mapped area, so it goes back and
tries xrstor again. It will spin in this loop forever.
Instead, fault in the maximum size which can be touched by XRSTOR (taken
from fpstate->user_size).
[ dhansen: tweak subject / changelog ]
Fixes: fcb3635f5018 ("x86/fpu/signal: Handle #PF in the direct restore path")
Reported-by: Konstantin Bogomolov <bogomolov@xxxxxxxxxx>
Suggested-by: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
Signed-off-by: Andrei Vagin <avagin@xxxxxxxxxx>
Signed-off-by: Dave Hansen <dave.hansen@xxxxxxxxxxxxxxx>
Cc:stable@xxxxxxxxxxxxxxx
Link: https://lore.kernel.org/all/20240130063603.3392627-1-avagin%40google.com
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
---
arch/x86/kernel/fpu/signal.c | 13 +++++--------
1 file changed, 5 insertions(+), 8 deletions(-)
--- a/arch/x86/kernel/fpu/signal.c
+++ b/arch/x86/kernel/fpu/signal.c
@@ -274,12 +274,13 @@ static int __restore_fpregs_from_user(vo
* Attempt to restore the FPU registers directly from user memory.
* Pagefaults are handled and any errors returned are fatal.
*/
-static bool restore_fpregs_from_user(void __user *buf, u64 xrestore,
- bool fx_only, unsigned int size)
+static bool restore_fpregs_from_user(void __user *buf, u64 xrestore, bool fx_only)
{
struct fpu *fpu = ¤t->thread.fpu;
int ret;
+ /* Restore enabled features only. */
+ xrestore &= fpu->fpstate->user_xfeatures;
retry:
fpregs_lock();
/* Ensure that XFD is up to date */
@@ -309,7 +310,7 @@ retry:
if (ret != X86_TRAP_PF)
return false;
- if (!fault_in_readable(buf, size))
+ if (!fault_in_readable(buf, fpu->fpstate->user_size))
goto retry;
return false;
}
@@ -339,7 +340,6 @@ static bool __fpu_restore_sig(void __use
struct user_i387_ia32_struct env;
bool success, fx_only = false;
union fpregs_state *fpregs;
- unsigned int state_size;
u64 user_xfeatures = 0;
if (use_xsave()) {
@@ -349,17 +349,14 @@ static bool __fpu_restore_sig(void __use
return false;
fx_only = !fx_sw_user.magic1;
- state_size = fx_sw_user.xstate_size;
user_xfeatures = fx_sw_user.xfeatures;
} else {
user_xfeatures = XFEATURE_MASK_FPSSE;
- state_size = fpu->fpstate->user_size;
}
if (likely(!ia32_fxstate)) {
/* Restore the FPU registers directly from user memory. */
- return restore_fpregs_from_user(buf_fx, user_xfeatures, fx_only,
- state_size);
+ return restore_fpregs_from_user(buf_fx, user_xfeatures, fx_only);
}
/*
Patches currently in stable-queue which might be from avagin@xxxxxxxxxx are
queue-6.6/x86-fpu-stop-relying-on-userspace-for-info-to-fault-in-xsave-buffer.patch
