Re: [PATCH v2] powerpc/ptrace: Split gpr32_set_common
From: Michael Ellerman
Date: Wed Aug 16 2023 - 01:43:05 EST
Christophe Leroy <christophe.leroy@xxxxxxxxxx> writes:
> objtool report the following warning:
>
> arch/powerpc/kernel/ptrace/ptrace-view.o: warning: objtool:
> gpr32_set_common+0x23c (.text+0x860): redundant UACCESS disable
>
> gpr32_set_common() conditionnaly opens and closes UACCESS based on
> whether kbuf point is NULL or not. This is wackelig.
>
> Split gpr32_set_common() in two fonctions, one for user one for
> kernel.
>
> Signed-off-by: Christophe Leroy <christophe.leroy@xxxxxxxxxx>
> ---
> v2: Mark gpr32_set_common_kernel() and gpr32_set_common_user() static
> ---
> arch/powerpc/kernel/ptrace/ptrace-view.c | 106 ++++++++++++++---------
> 1 file changed, 67 insertions(+), 39 deletions(-)
>
> diff --git a/arch/powerpc/kernel/ptrace/ptrace-view.c b/arch/powerpc/kernel/ptrace/ptrace-view.c
> index 3910cd7bb2d9..42abbed452cd 100644
> --- a/arch/powerpc/kernel/ptrace/ptrace-view.c
> +++ b/arch/powerpc/kernel/ptrace/ptrace-view.c
> @@ -716,73 +716,89 @@ int gpr32_get_common(struct task_struct *target,
> return membuf_zero(&to, (ELF_NGREG - PT_REGS_COUNT) * sizeof(u32));
> }
>
> -int gpr32_set_common(struct task_struct *target,
> - const struct user_regset *regset,
> - unsigned int pos, unsigned int count,
> - const void *kbuf, const void __user *ubuf,
> - unsigned long *regs)
> +static int gpr32_set_common_kernel(struct task_struct *target,
> + const struct user_regset *regset,
> + unsigned int pos, unsigned int count,
> + const void *kbuf, unsigned long *regs)
> {
> const compat_ulong_t *k = kbuf;
> +
> + pos /= sizeof(compat_ulong_t);
> + count /= sizeof(compat_ulong_t);
> +
> + for (; count > 0 && pos < PT_MSR; --count)
> + regs[pos++] = *k++;
> +
> + if (count > 0 && pos == PT_MSR) {
> + set_user_msr(target, *k++);
> + ++pos;
> + --count;
> + }
> +
> + for (; count > 0 && pos <= PT_MAX_PUT_REG; --count)
> + regs[pos++] = *k++;
> + for (; count > 0 && pos < PT_TRAP; --count, ++pos)
> + ++k;
> +
> + if (count > 0 && pos == PT_TRAP) {
> + set_user_trap(target, *k++);
> + ++pos;
> + --count;
> + }
> +
> + kbuf = k;
> + pos *= sizeof(compat_ulong_t);
> + count *= sizeof(compat_ulong_t);
> + user_regset_copyin_ignore(&pos, &count, &kbuf, NULL,
> + (PT_TRAP + 1) * sizeof(compat_ulong_t), -1);
> + return 0;
> +}
> +
> +static int gpr32_set_common_user(struct task_struct *target,
> + const struct user_regset *regset,
> + unsigned int pos, unsigned int count,
> + const void __user *ubuf, unsigned long *regs)
> +{
> const compat_ulong_t __user *u = ubuf;
> compat_ulong_t reg;
>
> - if (!kbuf && !user_read_access_begin(u, count))
> + if (!user_read_access_begin(u, count))
> return -EFAULT;
>
> pos /= sizeof(reg);
> count /= sizeof(reg);
>
> - if (kbuf)
> - for (; count > 0 && pos < PT_MSR; --count)
> - regs[pos++] = *k++;
> - else
> - for (; count > 0 && pos < PT_MSR; --count) {
> - unsafe_get_user(reg, u++, Efault);
> - regs[pos++] = reg;
> - }
> -
> + for (; count > 0 && pos < PT_MSR; --count) {
> + unsafe_get_user(reg, u++, Efault);
> + regs[pos++] = reg;
> + }
>
> if (count > 0 && pos == PT_MSR) {
> - if (kbuf)
> - reg = *k++;
> - else
> - unsafe_get_user(reg, u++, Efault);
> + unsafe_get_user(reg, u++, Efault);
> set_user_msr(target, reg);
> ++pos;
> --count;
> }
>
> - if (kbuf) {
> - for (; count > 0 && pos <= PT_MAX_PUT_REG; --count)
> - regs[pos++] = *k++;
> - for (; count > 0 && pos < PT_TRAP; --count, ++pos)
> - ++k;
> - } else {
> - for (; count > 0 && pos <= PT_MAX_PUT_REG; --count) {
> - unsafe_get_user(reg, u++, Efault);
> - regs[pos++] = reg;
> - }
> - for (; count > 0 && pos < PT_TRAP; --count, ++pos)
> - unsafe_get_user(reg, u++, Efault);
> + for (; count > 0 && pos <= PT_MAX_PUT_REG; --count) {
> + unsafe_get_user(reg, u++, Efault);
> + regs[pos++] = reg;
> }
> + for (; count > 0 && pos < PT_TRAP; --count, ++pos)
> + unsafe_get_user(reg, u++, Efault);
>
> if (count > 0 && pos == PT_TRAP) {
> - if (kbuf)
> - reg = *k++;
> - else
> - unsafe_get_user(reg, u++, Efault);
> + unsafe_get_user(reg, u++, Efault);
> set_user_trap(target, reg);
> ++pos;
> --count;
> }
> - if (!kbuf)
> - user_read_access_end();
> + user_read_access_end();
>
> - kbuf = k;
> ubuf = u;
> pos *= sizeof(reg);
> count *= sizeof(reg);
> - user_regset_copyin_ignore(&pos, &count, &kbuf, &ubuf,
> + user_regset_copyin_ignore(&pos, &count, NULL, &ubuf,
> (PT_TRAP + 1) * sizeof(reg), -1);
> return 0;
This was oopsing:
[ 1508.081530][T16432] BUG: Kernel NULL pointer dereference on read at 0x00000000
[ 1508.081551][T16432] Faulting instruction address: 0xc00000000002c690
[ 1508.081558][T16432] Oops: Kernel access of bad area, sig: 11 [#2]
[ 1508.081565][T16432] BE PAGE_SIZE=64K MMU=Hash SMP NR_CPUS=64 NUMA pSeries
[ 1508.081573][T16432] Modules linked in:
[ 1508.081580][T16432] CPU: 0 PID: 16432 Comm: ptrace-gpr Tainted: G D 6.5.0-rc3-00069-gb23dade91efd #1
[ 1508.081589][T16432] Hardware name: IBM,9117-MMA POWER6 (raw) 0x3e0301 0xf000002 of:IBM,EM350_176 hv:phyp pSeries
[ 1508.081597][T16432] NIP: c00000000002c690 LR: c00000000002f0f0 CTR: 0000000000000000
[ 1508.081604][T16432] REGS: c00000002000ba80 TRAP: 0300 Tainted: G D (6.5.0-rc3-00069-gb23dade91efd)
[ 1508.081612][T16432] MSR: 8000000000009032 <SF,EE,ME,IR,DR,RI> CR: 24004224 XER: 00000000
[ 1508.081632][T16432] CFAR: c00000000002c82c DAR: 0000000000000000 DSISR: 40000000 IRQMASK: 0
[ 1508.081632][T16432] GPR00: c00000000002f0f0 c00000002000bd20 c000000001347e00 c00000002116ab80
[ 1508.081632][T16432] GPR04: 0000000000000005 0000000010030270 000000000000002d c00000002aa3bfb0
[ 1508.081632][T16432] GPR08: c00000002aa3be80 0000000000000000 0000000000000000 0000000000000000
[ 1508.081632][T16432] GPR12: c00000000002d370 c0000000019f0000 0000000000000000 0000000000000000
[ 1508.081632][T16432] GPR16: 0000000000000000 0000000000000000 0000000000000000 0000000000000000
[ 1508.081632][T16432] GPR20: 0000000000000000 0000000000000000 0000000000000000 0000000000000000
[ 1508.081632][T16432] GPR24: 0000000000000000 0000000000000000 0000000000000000 0000000000000000
[ 1508.081632][T16432] GPR28: 00000000100301d0 00000000100301d0 000000000000000c 00000000000000a4
[ 1508.081735][T16432] NIP [c00000000002c690] gpr32_set_common_user.isra.0+0x160/0x490
[ 1508.081748][T16432] LR [c00000000002f0f0] compat_arch_ptrace+0x4a0/0xaf0
[ 1508.081756][T16432] Call Trace:
[ 1508.081760][T16432] [c00000002000bd20] [c00000002000bd60] 0xc00000002000bd60 (unreliable)
[ 1508.081771][T16432] [c00000002000bd50] [c00000000002f0f0] compat_arch_ptrace+0x4a0/0xaf0
[ 1508.081781][T16432] [c00000002000bdc0] [c000000000176734] compat_sys_ptrace+0x174/0x1e0
[ 1508.081791][T16432] [c00000002000be10] [c00000000002b404] system_call_exception+0x374/0x380
[ 1508.081803][T16432] [c00000002000be50] [c00000000000cb54] system_call_common+0xf4/0x258
Because user_regset_copyin_ignore() always dereferences kbuf:
static inline void user_regset_copyin_ignore(unsigned int *pos,
unsigned int *count,
const void **kbuf,
const void __user **ubuf,
const int start_pos,
const int end_pos)
{
if (*count == 0)
return;
BUG_ON(*pos < start_pos);
if (end_pos < 0 || *pos < end_pos) {
unsigned int copy = (end_pos < 0 ? *count
: min(*count, end_pos - *pos));
if (*kbuf)
*kbuf += copy;
I fixed it with:
diff --git a/arch/powerpc/kernel/ptrace/ptrace-view.c b/arch/powerpc/kernel/ptrace/ptrace-view.c
index 42abbed452cd..584cf5c3df50 100644
--- a/arch/powerpc/kernel/ptrace/ptrace-view.c
+++ b/arch/powerpc/kernel/ptrace/ptrace-view.c
@@ -760,6 +760,7 @@ static int gpr32_set_common_user(struct task_struct *target,
const void __user *ubuf, unsigned long *regs)
{
const compat_ulong_t __user *u = ubuf;
+ const void *kbuf = NULL;
compat_ulong_t reg;
if (!user_read_access_begin(u, count))
@@ -798,7 +799,7 @@ static int gpr32_set_common_user(struct task_struct *target,
ubuf = u;
pos *= sizeof(reg);
count *= sizeof(reg);
- user_regset_copyin_ignore(&pos, &count, NULL, &ubuf,
+ user_regset_copyin_ignore(&pos, &count, &kbuf, &ubuf,
(PT_TRAP + 1) * sizeof(reg), -1);
return 0;
cheers