Re: [PATCH] Fix msr check in compat_sys_swapcontext

Paul Mackerras <paulus@xxxxxxxxx> writes:

Andreas Schwab writes:

Paul Mackerras <paulus@xxxxxxxxx> 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.

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Andreas Schwab, SuSE Labs, schwab@xxxxxxx
SuSE Linux Products GmbH, Maxfeldstraße 5, 90409 Nürnberg, Germany
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