linux-kernel - [PATCH] powerpc/32: Fix FPR index validation and fpscr access

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Message-Id: <20220610080159.190353-1-ariel.miculas@belden.com>
Date:   Fri, 10 Jun 2022 11:01:59 +0300
From:   Ariel Miculas <ariel.miculas@...den.com>
To:     linuxppc-dev@...ts.ozlabs.org, linuxppc-dev@...abs.org,
        mpe@...erman.id.au, benh@...nel.crashing.org, paulus@...ba.org,
        linux-kernel@...r.kernel.org
Cc:     Ariel Miculas <ariel.miculas@...den.com>
Subject: [PATCH] powerpc/32: Fix FPR index validation and fpscr access

On PPC32, there are two indexes used for each FPR.

The last two indexes into the imaginary address space "USER area" are
used to access fpscr instead of the FPR registers. Fix the validation
condition so that the access of the FPR array doesn't overflow into
fpscr.  Also split the access of fpscr into high part and low part.

Signed-off-by: Ariel Miculas <ariel.miculas@...den.com>
---
 arch/powerpc/kernel/ptrace/ptrace-fpu.c | 24 ++++++++++++++++--------
 1 file changed, 16 insertions(+), 8 deletions(-)

diff --git a/arch/powerpc/kernel/ptrace/ptrace-fpu.c b/arch/powerpc/kernel/ptrace/ptrace-fpu.c
index 09c49632bfe5..eabc05b439f1 100644
--- a/arch/powerpc/kernel/ptrace/ptrace-fpu.c
+++ b/arch/powerpc/kernel/ptrace/ptrace-fpu.c
@@ -17,14 +17,18 @@ int ptrace_get_fpr(struct task_struct *child, int index, unsigned long *data)
 
 #ifdef CONFIG_PPC_FPU_REGS
 	flush_fp_to_thread(child);
-	if (fpidx < (PT_FPSCR - PT_FPR0)) {
-		if (IS_ENABLED(CONFIG_PPC32))
+	if (IS_ENABLED(CONFIG_PPC32)) {
+		if ((fpidx >> 1) < (PT_FPSCR - PT_FPR0) >> 1)
 			// On 32-bit the index we are passed refers to 32-bit words
 			*data = ((u32 *)child->thread.fp_state.fpr)[fpidx];
 		else
+			*data = ((u32 *)&child->thread.fp_state.fpscr)[fpidx & 1];
+	} else {
+		if (fpidx < (PT_FPSCR - PT_FPR0))
 			memcpy(data, &child->thread.TS_FPR(fpidx), sizeof(long));
-	} else
-		*data = child->thread.fp_state.fpscr;
+		else
+			*data = child->thread.fp_state.fpscr;
+	}
 #else
 	*data = 0;
 #endif
@@ -43,14 +47,18 @@ int ptrace_put_fpr(struct task_struct *child, int index, unsigned long data)
 
 #ifdef CONFIG_PPC_FPU_REGS
 	flush_fp_to_thread(child);
-	if (fpidx < (PT_FPSCR - PT_FPR0)) {
-		if (IS_ENABLED(CONFIG_PPC32))
+	if (IS_ENABLED(CONFIG_PPC32)) {
+		if ((fpidx >> 1) < (PT_FPSCR - PT_FPR0) >> 1)
 			// On 32-bit the index we are passed refers to 32-bit words
 			((u32 *)child->thread.fp_state.fpr)[fpidx] = data;
 		else
+			((u32 *)&child->thread.fp_state.fpscr)[fpidx & 1] = data;
+	} else {
+		if (fpidx < (PT_FPSCR - PT_FPR0))
 			memcpy(&child->thread.TS_FPR(fpidx), &data, sizeof(long));
-	} else
-		child->thread.fp_state.fpscr = data;
+		else
+			child->thread.fp_state.fpscr = data;
+	}
 #endif
 
 	return 0;
-- 
2.36.1