Re: [PATCH] powerpc/ptrace: Fix buffer overflow when handling PTRACE_PEEKUSER and PTRACE_POKEUSER
From: Christophe Leroy <hidden>
Date: 2022-06-11 09:08:10
Le 09/06/2022 à 11:52, Ariel Miculas a écrit :
quoted hunk ↗ jump to hunk
This fixes the gdbserver issue on PPC32 described here: Link: https://linuxppc-dev.ozlabs.narkive.com/C46DRek4/debug-problems-on-ppc-83xx-target-due-to-changed-struct-task-struct On PPC32, the user space code considers the floating point to be an array of unsigned int (32 bits) - the index passed in is based on this assumption. fp_state is a matrix consisting of 32 lines /* FP and VSX 0-31 register set / struct thread_fp_state { u64 fpr[32][TS_FPRWIDTH] attribute((aligned(16))); u64 fpscr; / Floating point status */ }; On PPC32, PT_FPSCR is defined as: (PT_FPR0 + 2*32 + 1) This means the fpr index validation allows a range from 0 to 65, leading to out-of-bounds array access. This ends up corrupting threads_struct->state, which holds the state of the task. Thus, threads incorrectly transition from a running state to a traced state and get stuck in that state. On PPC32 it's ok to assume that TS_FPRWIDTH is 1 because CONFIG_VSX is PPC64 specific. TS_FPROFFSET can be safely ignored, thus the assumption that fpr is an array of 32 elements of type u64 holds true. Solution taken from arch/powerpc/kernel/ptrace32.c Signed-off-by: Ariel Miculas <redacted> --- arch/powerpc/kernel/ptrace/ptrace-fpu.c | 31 +++++++++++++++++++++++-- 1 file changed, 29 insertions(+), 2 deletions(-)diff --git a/arch/powerpc/kernel/ptrace/ptrace-fpu.c b/arch/powerpc/kernel/ptrace/ptrace-fpu.c index 5dca19361316..93695abbbdfb 100644 --- a/arch/powerpc/kernel/ptrace/ptrace-fpu.c +++ b/arch/powerpc/kernel/ptrace/ptrace-fpu.c@@ -6,9 +6,16 @@ #include "ptrace-decl.h" +#ifdef CONFIG_PPC32 +/* Macros to workout the correct index for the FPR in the thread struct */ +#define FPRNUMBER(i) (((i) - PT_FPR0) >> 1) +#define FPRHALF(i) (((i) - PT_FPR0) & 1) +#define FPRINDEX(i) TS_FPRWIDTH * FPRNUMBER(i) * 2 + FPRHALF(i) +#endif
I can't see the benefit of such macros if they are only for PPC32.
+
int ptrace_get_fpr(struct task_struct *child, int index, unsigned long *data)
{
-#ifdef CONFIG_PPC_FPU_REGS
+#if defined(CONFIG_PPC_FPU_REGS) && !defined(CONFIG_PPC32)
unsigned int fpidx = index - PT_FPR0;
#endif#ifdefs should be avoided as much as possible.
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@@ -17,10 +24,20 @@ int ptrace_get_fpr(struct task_struct *child, int index, unsigned long *data) #ifdef CONFIG_PPC_FPU_REGS flush_fp_to_thread(child); +#ifdef CONFIG_PPC32
Here you could use IS_ENABLED(CONFIG_PPC32), it would also avoid the above #ifdef.
+ /* + * the user space code considers the floating point + * to be an array of unsigned int (32 bits) - the + * index passed in is based on this assumption. + */ + *data = ((unsigned int *)child->thread.fp_state.fpr) + [FPRINDEX(index)];
if I understand FPRINDEX(index) correctly, at the end we have FPRINDEX(i) == i, so I can't see the point. Michael's patch seems easier to understand. I think if one day we want something common to ppc32 and ppc64, we need to use a new macro similar to TS_FPR() but that properly takes ppc32 into account. Pay attention to not change TS_FPR() as it is used in other places where it is valid for both PPC32 and PPC64.
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+#else if (fpidx < (PT_FPSCR - PT_FPR0)) memcpy(data, &child->thread.TS_FPR(fpidx), sizeof(long)); else *data = child->thread.fp_state.fpscr; +#endif #else *data = 0; #endif@@ -30,7 +47,7 @@ int ptrace_get_fpr(struct task_struct *child, int index, unsigned long *data) int ptrace_put_fpr(struct task_struct *child, int index, unsigned long data) { -#ifdef CONFIG_PPC_FPU_REGS +#if defined(CONFIG_PPC_FPU_REGS) && !defined(CONFIG_PPC32) unsigned int fpidx = index - PT_FPR0; #endif@@ -39,10 +56,20 @@ int ptrace_put_fpr(struct task_struct *child, int index, unsigned long data) #ifdef CONFIG_PPC_FPU_REGS flush_fp_to_thread(child); +#ifdef CONFIG_PPC32 + /* + * the user space code considers the floating point + * to be an array of unsigned int (32 bits) - the + * index passed in is based on this assumption. + */ + ((unsigned int *)child->thread.fp_state.fpr) + [FPRINDEX(index)] = data; +#else if (fpidx < (PT_FPSCR - PT_FPR0)) memcpy(&child->thread.TS_FPR(fpidx), &data, sizeof(long)); else child->thread.fp_state.fpscr = data; +#endif #endif return 0;