2008-11-05 12:31:14

by Andreas Schwab

Subject: [PATCH] Fix msr check in compat_sys_swapcontext

The new context may not be 16-byte aligned, so the real address of the
mcontext structure should be read from the uc_regs pointer instead of
directly using the (unaligned) uc_mcontext field.

Signed-off-by: Andreas Schwab <[email protected]>

---
diff --git a/arch/powerpc/kernel/signal_32.c b/arch/powerpc/kernel/signal_32.c
index a6a4310..dc10720 100644
--- a/arch/powerpc/kernel/signal_32.c
+++ b/arch/powerpc/kernel/signal_32.c
@@ -941,9 +941,17 @@ long sys_swapcontext(struct ucontext __user *old_ctx,
#ifdef CONFIG_PPC64
unsigned long new_msr = 0;

- if (new_ctx &&
- get_user(new_msr, &new_ctx->uc_mcontext.mc_gregs[PT_MSR]))
- return -EFAULT;
+ if (new_ctx) {
+ struct mcontext __user *mcp;
+ u32 cmcp;
+
+ /* Get pointer to the real mcontext. */
+ if (__get_user(cmcp, &new_ctx->uc_regs))
+ return -EFAULT;
+ mcp = (struct mcontext __user *)(u64)cmcp;
+ if (__get_user(new_msr, &mcp->mc_gregs[PT_MSR]))
+ return -EFAULT;
+ }
/*
* Check that the context is not smaller than the original
* size (with VMX but without VSX)

--
Andreas Schwab, SuSE Labs, [email protected]
SuSE Linux Products GmbH, Maxfeldstra?e 5, 90409 N?rnberg, Germany
PGP key fingerprint = 58CA 54C7 6D53 942B 1756 01D3 44D5 214B 8276 4ED5
"And now for something completely different."

2008-11-06 00:52:34

by Paul Mackerras

Subject: Re: [PATCH] Fix msr check in compat_sys_swapcontext

Andreas Schwab writes:

> The new context may not be 16-byte aligned, so the real address of the
> mcontext structure should be read from the uc_regs pointer instead of
> directly using the (unaligned) uc_mcontext field.

Good catch, but...

> @@ -941,9 +941,17 @@ long sys_swapcontext(struct ucontext __user *old_ctx,
> #ifdef CONFIG_PPC64
> unsigned long new_msr = 0;
>
> - if (new_ctx &&
> - get_user(new_msr, &new_ctx->uc_mcontext.mc_gregs[PT_MSR]))
> - return -EFAULT;
> + if (new_ctx) {
> + struct mcontext __user *mcp;
> + u32 cmcp;
> +
> + /* Get pointer to the real mcontext. */
> + if (__get_user(cmcp, &new_ctx->uc_regs))

we need to use get_user, not __get_user, since we haven't done an
access_ok() check on the address.

> + return -EFAULT;
> + mcp = (struct mcontext __user *)(u64)cmcp;
> + if (__get_user(new_msr, &mcp->mc_gregs[PT_MSR]))

ditto here.

Paul.

2008-11-06 09:23:29

by Andreas Schwab

Subject: Re: [PATCH] Fix msr check in compat_sys_swapcontext

Paul Mackerras <[email protected]> writes:

> we need to use get_user, not __get_user, since we haven't done an
> access_ok() check on the address.

The address is always ok since its a compat pointer, see do_setcontext.

Andreas.

--
Andreas Schwab, SuSE Labs, [email protected]
SuSE Linux Products GmbH, Maxfeldstra?e 5, 90409 N?rnberg, Germany
PGP key fingerprint = 58CA 54C7 6D53 942B 1756 01D3 44D5 214B 8276 4ED5
"And now for something completely different."

2008-11-06 10:40:45

by Paul Mackerras

Subject: Re: [PATCH] Fix msr check in compat_sys_swapcontext

Andreas Schwab writes:

> Paul Mackerras <[email protected]> writes:
>
> > we need to use get_user, not __get_user, since we haven't done an
> > access_ok() check on the address.
>
> The address is always ok since its a compat pointer, see do_setcontext.

OK, since it's inside a CONFIG_PPC64 block. I'll add a paragraph to
the patch description pointing that out.

Paul.

2008-11-06 10:49:24

by Andreas Schwab

Subject: Re: [PATCH] Fix msr check in compat_sys_swapcontext

Paul Mackerras <[email protected]> writes:

> Andreas Schwab writes:
>
>> Paul Mackerras <[email protected]> writes:
>>
>> > we need to use get_user, not __get_user, since we haven't done an
>> > access_ok() check on the address.
>>
>> The address is always ok since its a compat pointer, see do_setcontext.
>
> OK, since it's inside a CONFIG_PPC64 block. I'll add a paragraph to
> the patch description pointing that out.

How about this:

diff --git a/arch/powerpc/kernel/signal_32.c b/arch/powerpc/kernel/signal_32.c
index a6a4310..b13abf3 100644
--- a/arch/powerpc/kernel/signal_32.c
+++ b/arch/powerpc/kernel/signal_32.c
@@ -941,9 +941,21 @@ long sys_swapcontext(struct ucontext __user *old_ctx,
#ifdef CONFIG_PPC64
unsigned long new_msr = 0;

- if (new_ctx &&
- get_user(new_msr, &new_ctx->uc_mcontext.mc_gregs[PT_MSR]))
- return -EFAULT;
+ if (new_ctx) {
+ struct mcontext __user *mcp;
+ u32 cmcp;
+
+ /*
+ * Get pointer to the real mcontext. No need for
+ * access_ok since we are dealing with compat
+ * pointers.
+ */
+ if (__get_user(cmcp, &new_ctx->uc_regs))
+ return -EFAULT;
+ mcp = (struct mcontext __user *)(u64)cmcp;
+ if (__get_user(new_msr, &mcp->mc_gregs[PT_MSR]))
+ return -EFAULT;
+ }
/*
* Check that the context is not smaller than the original
* size (with VMX but without VSX)

Andreas.

--
Andreas Schwab, SuSE Labs, [email protected]
SuSE Linux Products GmbH, Maxfeldstra?e 5, 90409 N?rnberg, Germany
PGP key fingerprint = 58CA 54C7 6D53 942B 1756 01D3 44D5 214B 8276 4ED5
"And now for something completely different."