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x86/mm: Fix fault error path using unsafe vma pointer

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commit 7b2d0dbac4 ("x86/mm/pkeys: Pass VMA down in to fault signal
generation code") passes down a vma pointer to the error path, but that is
done once the mmap_sem is released when calling mm_fault_error() from
__do_page_fault().

This is dangerous as the vma structure is no more safe to be used once the
mmap_sem has been released. As only the protection key value is required in
the error processing, we could just pass down this value.

Fix it by passing a pointer to a protection key value down to the fault
signal generation code. The use of a pointer allows to keep the check
generating a warning message in fill_sig_info_pkey() when the vma was not
known. If the pointer is valid, the protection value can be accessed by
deferencing the pointer.

[ tglx: Made *pkey u32 as that's the type which is passed in siginfo ]

Fixes: 7b2d0dbac4 ("x86/mm/pkeys: Pass VMA down in to fault signal generation code")
Signed-off-by: Laurent Dufour <ldufour@linux.vnet.ibm.com>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Cc: linux-mm@kvack.org
Cc: Dave Hansen <dave.hansen@linux.intel.com>
Cc: stable@vger.kernel.org
Link: http://lkml.kernel.org/r/1504513935-12742-1-git-send-email-ldufour@linux.vnet.ibm.com
This commit is contained in:
Laurent Dufour 2017-09-04 10:32:15 +02:00 committed by Thomas Gleixner
parent 10430364eb
commit a3c4fb7c9c
1 changed files with 24 additions and 23 deletions
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47
arch/x86/mm/fault.c
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@ -192,8 +192,7 @@ is_prefetch(struct pt_regs *regs, unsigned long error_code, unsigned long addr)
* 6. T1 : reaches here, sees vma_pkey(vma)=5, when we really
* faulted on a pte with its pkey=4.
*/
static void fill_sig_info_pkey(int si_code, siginfo_t *info,
struct vm_area_struct *vma)
static void fill_sig_info_pkey(int si_code, siginfo_t *info, u32 *pkey)
{
/* This is effectively an #ifdef */
if (!boot_cpu_has(X86_FEATURE_OSPKE))
@ -209,7 +208,7 @@ static void fill_sig_info_pkey(int si_code, siginfo_t *info,
* valid VMA, so we should never reach this without a
* valid VMA.
*/
if (!vma) {
if (!pkey) {
WARN_ONCE(1, "PKU fault with no VMA passed in");
info->si_pkey = 0;
return;
@ -219,13 +218,12 @@ static void fill_sig_info_pkey(int si_code, siginfo_t *info,
* absolutely guranteed to be 100% accurate because of
* the race explained above.
*/
info->si_pkey = vma_pkey(vma);
info->si_pkey = *pkey;
}
static void
force_sig_info_fault(int si_signo, int si_code, unsigned long address,
struct task_struct *tsk, struct vm_area_struct *vma,
int fault)
struct task_struct *tsk, u32 *pkey, int fault)
{
unsigned lsb = 0;
siginfo_t info;
@ -240,7 +238,7 @@ force_sig_info_fault(int si_signo, int si_code, unsigned long address,
lsb = PAGE_SHIFT;
info.si_addr_lsb = lsb;
fill_sig_info_pkey(si_code, &info, vma);
fill_sig_info_pkey(si_code, &info, pkey);
force_sig_info(si_signo, &info, tsk);
}
@ -762,8 +760,6 @@ no_context(struct pt_regs *regs, unsigned long error_code,
struct task_struct *tsk = current;
unsigned long flags;
int sig;
/* No context means no VMA to pass down */
struct vm_area_struct *vma = NULL;
/* Are we prepared to handle this kernel fault? */
if (fixup_exception(regs, X86_TRAP_PF)) {
@ -788,7 +784,7 @@ no_context(struct pt_regs *regs, unsigned long error_code,
/* XXX: hwpoison faults will set the wrong code. */
force_sig_info_fault(signal, si_code, address,
tsk, vma, 0);
tsk, NULL, 0);
}
/*
@ -896,8 +892,7 @@ show_signal_msg(struct pt_regs *regs, unsigned long error_code,
static void
__bad_area_nosemaphore(struct pt_regs *regs, unsigned long error_code,
unsigned long address, struct vm_area_struct *vma,
int si_code)
unsigned long address, u32 *pkey, int si_code)
{
struct task_struct *tsk = current;
@ -945,7 +940,7 @@ __bad_area_nosemaphore(struct pt_regs *regs, unsigned long error_code,
tsk->thread.error_code = error_code;
tsk->thread.trap_nr = X86_TRAP_PF;
force_sig_info_fault(SIGSEGV, si_code, address, tsk, vma, 0);
force_sig_info_fault(SIGSEGV, si_code, address, tsk, pkey, 0);
return;
}
@ -958,9 +953,9 @@ __bad_area_nosemaphore(struct pt_regs *regs, unsigned long error_code,
static noinline void
bad_area_nosemaphore(struct pt_regs *regs, unsigned long error_code,
unsigned long address, struct vm_area_struct *vma)
unsigned long address, u32 *pkey)
{
__bad_area_nosemaphore(regs, error_code, address, vma, SEGV_MAPERR);
__bad_area_nosemaphore(regs, error_code, address, pkey, SEGV_MAPERR);
}
static void
@ -968,6 +963,10 @@ __bad_area(struct pt_regs *regs, unsigned long error_code,
unsigned long address, struct vm_area_struct *vma, int si_code)
{
struct mm_struct *mm = current->mm;
u32 pkey;
if (vma)
pkey = vma_pkey(vma);
/*
* Something tried to access memory that isn't in our memory map..
@ -975,7 +974,8 @@ __bad_area(struct pt_regs *regs, unsigned long error_code,
*/
up_read(&mm->mmap_sem);
__bad_area_nosemaphore(regs, error_code, address, vma, si_code);
__bad_area_nosemaphore(regs, error_code, address,
(vma) ? &pkey : NULL, si_code);
}
static noinline void
@ -1018,7 +1018,7 @@ bad_area_access_error(struct pt_regs *regs, unsigned long error_code,
static void
do_sigbus(struct pt_regs *regs, unsigned long error_code, unsigned long address,
struct vm_area_struct *vma, unsigned int fault)
u32 *pkey, unsigned int fault)
{
struct task_struct *tsk = current;
int code = BUS_ADRERR;
@ -1045,13 +1045,12 @@ do_sigbus(struct pt_regs *regs, unsigned long error_code, unsigned long address,
code = BUS_MCEERR_AR;
}
#endif
force_sig_info_fault(SIGBUS, code, address, tsk, vma, fault);
force_sig_info_fault(SIGBUS, code, address, tsk, pkey, fault);
}
static noinline void
mm_fault_error(struct pt_regs *regs, unsigned long error_code,
unsigned long address, struct vm_area_struct *vma,
unsigned int fault)
unsigned long address, u32 *pkey, unsigned int fault)
{
if (fatal_signal_pending(current) && !(error_code & PF_USER)) {
no_context(regs, error_code, address, 0, 0);
@ -1075,9 +1074,9 @@ mm_fault_error(struct pt_regs *regs, unsigned long error_code,
} else {
if (fault & (VM_FAULT_SIGBUS|VM_FAULT_HWPOISON|
VM_FAULT_HWPOISON_LARGE))
do_sigbus(regs, error_code, address, vma, fault);
do_sigbus(regs, error_code, address, pkey, fault);
else if (fault & VM_FAULT_SIGSEGV)
bad_area_nosemaphore(regs, error_code, address, vma);
bad_area_nosemaphore(regs, error_code, address, pkey);
else
BUG();
}
@ -1267,6 +1266,7 @@ __do_page_fault(struct pt_regs *regs, unsigned long error_code,
struct mm_struct *mm;
int fault, major = 0;
unsigned int flags = FAULT_FLAG_ALLOW_RETRY | FAULT_FLAG_KILLABLE;
u32 pkey;
tsk = current;
mm = tsk->mm;
@ -1467,9 +1467,10 @@ good_area:
return;
}
pkey = vma_pkey(vma);
up_read(&mm->mmap_sem);
if (unlikely(fault & VM_FAULT_ERROR)) {
mm_fault_error(regs, error_code, address, vma, fault);
mm_fault_error(regs, error_code, address, &pkey, fault);
return;
}