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ARM: 8687/1: signal: Fix unparseable iwmmxt_sigframe in uc_regspace[]

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In kernels with CONFIG_IWMMXT=y running on non-iWMMXt hardware, the
signal frame can be left partially uninitialised in such a way
that userspace cannot parse uc_regspace[] safely.  In particular,
this means that the VFP registers cannot be located reliably in the
signal frame when a multi_v7_defconfig kernel is run on the
majority of platforms.

The cause is that the uc_regspace[] is laid out statically based on
the kernel config, but the decision of whether to save/restore the
iWMMXt registers must be a runtime decision.

To minimise breakage of software that may assume a fixed layout,
this patch emits a dummy block of the same size as iwmmxt_sigframe,
for non-iWMMXt threads.  However, the magic and size of this block
are now filled in to help parsers skip over it.  A new DUMMY_MAGIC
is defined for this purpose.

It is probably legitimate (if non-portable) for userspace to
manufacture its own sigframe for sigreturn, and there is no obvious
reason why userspace should be required to insert a DUMMY_MAGIC
block when running on non-iWMMXt hardware, when omitting it has
worked just fine forever in other configurations.  So in this case,
sigreturn does not require this block to be present.

Reported-by: Edmund Grimley-Evans <Edmund.Grimley-Evans@arm.com>
Signed-off-by: Dave Martin <Dave.Martin@arm.com>
Signed-off-by: Russell King <rmk+kernel@armlinux.org.uk>
This commit is contained in:
Dave Martin 2017-06-30 18:56:59 +01:00 committed by Russell King
parent 269583559c
commit ce184a0dee
2 changed files with 65 additions and 17 deletions
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6
arch/arm/include/asm/ucontext.h
View File

@ -35,6 +35,12 @@ struct ucontext {
* bytes, to prevent unpredictable padding in the signal frame.
*/
/*
* Dummy padding block: if this magic is encountered, the block should
* be skipped using the corresponding size field.
*/
#define DUMMY_MAGIC 0xb0d9ed01
#ifdef CONFIG_CRUNCH
#define CRUNCH_MAGIC 0x5065cf03
#define CRUNCH_STORAGE_SIZE (CRUNCH_SIZE + 8)

68
arch/arm/kernel/signal.c
View File

@ -40,8 +40,10 @@ static int preserve_crunch_context(struct crunch_sigframe __user *frame)
return __copy_to_user(frame, kframe, sizeof(*frame));
}
static int restore_crunch_context(struct crunch_sigframe __user *frame)
static int restore_crunch_context(char __user **auxp)
{
struct crunch_sigframe __user *frame =
(struct crunch_sigframe __user *)*auxp;
char kbuf[sizeof(*frame) + 8];
struct crunch_sigframe *kframe;
@ -52,6 +54,7 @@ static int restore_crunch_context(struct crunch_sigframe __user *frame)
if (kframe->magic != CRUNCH_MAGIC ||
kframe->size != CRUNCH_STORAGE_SIZE)
return -1;
*auxp += CRUNCH_STORAGE_SIZE;
crunch_task_restore(current_thread_info(), &kframe->storage);
return 0;
}
@ -63,17 +66,35 @@ static int preserve_iwmmxt_context(struct iwmmxt_sigframe __user *frame)
{
char kbuf[sizeof(*frame) + 8];
struct iwmmxt_sigframe *kframe;
int err = 0;
/* the iWMMXt context must be 64 bit aligned */
kframe = (struct iwmmxt_sigframe *)((unsigned long)(kbuf + 8) & ~7);
if (test_thread_flag(TIF_USING_IWMMXT)) {
kframe->magic = IWMMXT_MAGIC;
kframe->size = IWMMXT_STORAGE_SIZE;
iwmmxt_task_copy(current_thread_info(), &kframe->storage);
return __copy_to_user(frame, kframe, sizeof(*frame));
err = __copy_to_user(frame, kframe, sizeof(*frame));
} else {
/*
* For bug-compatibility with older kernels, some space
* has to be reserved for iWMMXt even if it's not used.
* Set the magic and size appropriately so that properly
* written userspace can skip it reliably:
*/
__put_user_error(DUMMY_MAGIC, &frame->magic, err);
__put_user_error(IWMMXT_STORAGE_SIZE, &frame->size, err);
}
static int restore_iwmmxt_context(struct iwmmxt_sigframe __user *frame)
return err;
}
static int restore_iwmmxt_context(char __user **auxp)
{
struct iwmmxt_sigframe __user *frame =
(struct iwmmxt_sigframe __user *)*auxp;
char kbuf[sizeof(*frame) + 8];
struct iwmmxt_sigframe *kframe;
@ -81,10 +102,28 @@ static int restore_iwmmxt_context(struct iwmmxt_sigframe __user *frame)
kframe = (struct iwmmxt_sigframe *)((unsigned long)(kbuf + 8) & ~7);
if (__copy_from_user(kframe, frame, sizeof(*frame)))
return -1;
if (kframe->magic != IWMMXT_MAGIC ||
kframe->size != IWMMXT_STORAGE_SIZE)
/*
* For non-iWMMXt threads: a single iwmmxt_sigframe-sized dummy
* block is discarded for compatibility with setup_sigframe() if
* present, but we don't mandate its presence. If some other
* magic is here, it's not for us:
*/
if (!test_thread_flag(TIF_USING_IWMMXT) &&
kframe->magic != DUMMY_MAGIC)
return 0;
if (kframe->size != IWMMXT_STORAGE_SIZE)
return -1;
if (test_thread_flag(TIF_USING_IWMMXT)) {
if (kframe->magic != IWMMXT_MAGIC)
return -1;
iwmmxt_task_restore(current_thread_info(), &kframe->storage);
}
*auxp += IWMMXT_STORAGE_SIZE;
return 0;
}
@ -107,8 +146,10 @@ static int preserve_vfp_context(struct vfp_sigframe __user *frame)
return vfp_preserve_user_clear_hwstate(&frame->ufp, &frame->ufp_exc);
}
static int restore_vfp_context(struct vfp_sigframe __user *frame)
static int restore_vfp_context(char __user **auxp)
{
struct vfp_sigframe __user *frame =
(struct vfp_sigframe __user *)*auxp;
unsigned long magic;
unsigned long size;
int err = 0;
@ -121,6 +162,7 @@ static int restore_vfp_context(struct vfp_sigframe __user *frame)
if (magic != VFP_MAGIC || size != VFP_STORAGE_SIZE)
return -EINVAL;
*auxp += size;
return vfp_restore_user_hwstate(&frame->ufp, &frame->ufp_exc);
}
@ -141,7 +183,7 @@ struct rt_sigframe {
static int restore_sigframe(struct pt_regs *regs, struct sigframe __user *sf)
{
struct aux_sigframe __user *aux;
char __user *aux;
sigset_t set;
int err;
@ -169,18 +211,18 @@ static int restore_sigframe(struct pt_regs *regs, struct sigframe __user *sf)
err |= !valid_user_regs(regs);
aux = (struct aux_sigframe __user *) sf->uc.uc_regspace;
aux = (char __user *) sf->uc.uc_regspace;
#ifdef CONFIG_CRUNCH
if (err == 0)
err |= restore_crunch_context(&aux->crunch);
err |= restore_crunch_context(&aux);
#endif
#ifdef CONFIG_IWMMXT
if (err == 0 && test_thread_flag(TIF_USING_IWMMXT))
err |= restore_iwmmxt_context(&aux->iwmmxt);
if (err == 0)
err |= restore_iwmmxt_context(&aux);
#endif
#ifdef CONFIG_VFP
if (err == 0)
err |= restore_vfp_context(&aux->vfp);
err |= restore_vfp_context(&aux);
#endif
return err;
@ -286,7 +328,7 @@ setup_sigframe(struct sigframe __user *sf, struct pt_regs *regs, sigset_t *set)
err |= preserve_crunch_context(&aux->crunch);
#endif
#ifdef CONFIG_IWMMXT
if (err == 0 && test_thread_flag(TIF_USING_IWMMXT))
if (err == 0)
err |= preserve_iwmmxt_context(&aux->iwmmxt);
#endif
#ifdef CONFIG_VFP