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Fix msr check in compat_sys_swapcontext

PATCH In review Andreas Schwab 2 participants 5 messages Nov 5, 2008 – Nov 6, 2008 PowerPC

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Andreas Schwab

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#0 lore raw

PATCH 1/1 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]>

---

arch/powerpc/kernel/signal_32.c +11 -3
index a6a4310..dc10720 100644
@@ -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)
Signature · 4 lines
Andreas Schwab, SuSE Labs, [email protected]
SuSE Linux Products GmbH, Maxfeldstraße 5, 90409 Nürnberg, Germany
PGP key fingerprint = 58CA 54C7 6D53 942B 1756  01D3 44D5 214B 8276 4ED5
"And now for something completely different."
#1 lore raw
Quoted 3 lines · Andreas Schwab

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...

arch/powerpc/kernel/signal_32.c long sys_swapcontext(struct ucontext __user *old_ctx, · line 949

Quoted 13 lines
arch/powerpc/kernel/signal_32.c +6 -3
@@ -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.

arch/powerpc/kernel/signal_32.c long sys_swapcontext(struct ucontext __user *old_ctx, · line 952

Quoted 3 lines
arch/powerpc/kernel/signal_32.c +3 -0
+			return -EFAULT;
+		mcp = (struct mcontext __user *)(u64)cmcp;
+		if (__get_user(new_msr, &mcp->mc_gregs[PT_MSR]))

ditto here.

Paul.

author
#2 lore raw
Quoted 2 lines · Paul Mackerras

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.

Signature · 4 lines
Andreas Schwab, SuSE Labs, [email protected]
SuSE Linux Products GmbH, Maxfeldstraße 5, 90409 Nürnberg, Germany
PGP key fingerprint = 58CA 54C7 6D53 942B 1756  01D3 44D5 214B 8276 4ED5
"And now for something completely different."
#3 lore raw
Quoted 6 lines · Andreas Schwab
Quoted 2 lines · Paul Mackerras

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.

author
#4 lore raw
Quoted 11 lines · Paul Mackerras
Quoted 6 lines · Andreas Schwab
Quoted 2 lines · Paul Mackerras

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:

arch/powerpc/kernel/signal_32.c +15 -3
index a6a4310..b13abf3 100644
@@ -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.

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