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authorMichael Ellerman <mpe@ellerman.id.au>2019-02-14 11:08:29 +1100
committerGreg Kroah-Hartman <gregkh@linuxfoundation.org>2019-03-23 13:19:52 +0100
commit380960e5a1a7c8b4f64959e4896885a2f2a31f19 (patch)
treeb57ec53e3ce7db06b74042fb0aff359a1ea3017c
parentb8f072b0f3d2df5cc582b4dfcde36989e18869da (diff)
powerpc/ptrace: Simplify vr_get/set() to avoid GCC warning
commit ca6d5149d2ad0a8d2f9c28cbe379802260a0a5e0 upstream. GCC 8 warns about the logic in vr_get/set(), which with -Werror breaks the build: In function ‘user_regset_copyin’, inlined from ‘vr_set’ at arch/powerpc/kernel/ptrace.c:628:9: include/linux/regset.h:295:4: error: ‘memcpy’ offset [-527, -529] is out of the bounds [0, 16] of object ‘vrsave’ with type ‘union <anonymous>’ [-Werror=array-bounds] arch/powerpc/kernel/ptrace.c: In function ‘vr_set’: arch/powerpc/kernel/ptrace.c:623:5: note: ‘vrsave’ declared here } vrsave; This has been identified as a regression in GCC, see GCC bug 88273. However we can avoid the warning and also simplify the logic and make it more robust. Currently we pass -1 as end_pos to user_regset_copyout(). This says "copy up to the end of the regset". The definition of the regset is: [REGSET_VMX] = { .core_note_type = NT_PPC_VMX, .n = 34, .size = sizeof(vector128), .align = sizeof(vector128), .active = vr_active, .get = vr_get, .set = vr_set }, The end is calculated as (n * size), ie. 34 * sizeof(vector128). In vr_get/set() we pass start_pos as 33 * sizeof(vector128), meaning we can copy up to sizeof(vector128) into/out-of vrsave. The on-stack vrsave is defined as: union { elf_vrreg_t reg; u32 word; } vrsave; And elf_vrreg_t is: typedef __vector128 elf_vrreg_t; So there is no bug, but we rely on all those sizes lining up, otherwise we would have a kernel stack exposure/overwrite on our hands. Rather than relying on that we can pass an explict end_pos based on the sizeof(vrsave). The result should be exactly the same but it's more obviously not over-reading/writing the stack and it avoids the compiler warning. Reported-by: Meelis Roos <mroos@linux.ee> Reported-by: Mathieu Malaterre <malat@debian.org> Cc: stable@vger.kernel.org Tested-by: Mathieu Malaterre <malat@debian.org> Tested-by: Meelis Roos <mroos@linux.ee> Signed-off-by: Michael Ellerman <mpe@ellerman.id.au> Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
-rw-r--r--arch/powerpc/kernel/ptrace.c10
1 files changed, 8 insertions, 2 deletions
diff --git a/arch/powerpc/kernel/ptrace.c b/arch/powerpc/kernel/ptrace.c
index adfa63e7df8c..4f2829634d79 100644
--- a/arch/powerpc/kernel/ptrace.c
+++ b/arch/powerpc/kernel/ptrace.c
@@ -547,6 +547,7 @@ static int vr_get(struct task_struct *target, const struct user_regset *regset,
/*
* Copy out only the low-order word of vrsave.
*/
+ int start, end;
union {
elf_vrreg_t reg;
u32 word;
@@ -555,8 +556,10 @@ static int vr_get(struct task_struct *target, const struct user_regset *regset,
vrsave.word = target->thread.vrsave;
+ start = 33 * sizeof(vector128);
+ end = start + sizeof(vrsave);
ret = user_regset_copyout(&pos, &count, &kbuf, &ubuf, &vrsave,
- 33 * sizeof(vector128), -1);
+ start, end);
}
return ret;
@@ -594,6 +597,7 @@ static int vr_set(struct task_struct *target, const struct user_regset *regset,
/*
* We use only the first word of vrsave.
*/
+ int start, end;
union {
elf_vrreg_t reg;
u32 word;
@@ -602,8 +606,10 @@ static int vr_set(struct task_struct *target, const struct user_regset *regset,
vrsave.word = target->thread.vrsave;
+ start = 33 * sizeof(vector128);
+ end = start + sizeof(vrsave);
ret = user_regset_copyin(&pos, &count, &kbuf, &ubuf, &vrsave,
- 33 * sizeof(vector128), -1);
+ start, end);
if (!ret)
target->thread.vrsave = vrsave.word;
}