[PATCH v3 15/15] powerpc: Implement UACCESS validation on PPC32
From: Christophe Leroy
Date: Fri Jun 23 2023 - 13:09:07 EST
In order to implement UACCESS validation, objtool support
for powerpc needs to be enhanced to decode more instructions.
It also requires implementation of switch tables finding.
On PPC32 it is similar to x86, switch tables are anonymous in .rodata,
the difference is that the value is relative to its index in the table.
Then comes the UACCESS enabling/disabling instructions. On booke and
8xx it is done with a mtspr instruction. For 8xx that's in SPRN_MD_AP,
for booke that's in SPRN_PID. Annotate those instructions.
For book3s/32 that's a bit more complex and left aside for the moment.
No work has been done for ASM files, they are not used for UACCESS
so for the moment just tell objtool to ignore ASM files.
For relocable code, the .got2 relocation preceding each global
function needs to be marked as ignored because some versions of GCC
do this:
120: 00 00 00 00 .long 0x0
120: R_PPC_REL32 .got2+0x7ff0
00000124 <tohex>:
124: 94 21 ff f0 stwu r1,-16(r1)
128: 7c 08 02 a6 mflr r0
12c: 42 9f 00 05 bcl 20,4*cr7+so,130 <tohex+0xc>
130: 39 00 00 00 li r8,0
134: 39 20 00 08 li r9,8
138: 93 c1 00 08 stw r30,8(r1)
13c: 7f c8 02 a6 mflr r30
140: 90 01 00 14 stw r0,20(r1)
144: 80 1e ff f0 lwz r0,-16(r30)
148: 7f c0 f2 14 add r30,r0,r30
14c: 81 5e 80 00 lwz r10,-32768(r30)
150: 80 fe 80 04 lwz r7,-32764(r30)
While other versions do that:
00000120 <tohex>:
120: 94 21 ff f0 stwu r1,-16(r1)
124: 7c 08 02 a6 mflr r0
128: 42 9f 00 05 bcl 20,4*cr7+so,12c <tohex+0xc>
12c: 39 00 00 00 li r8,0
130: 39 20 00 08 li r9,8
134: 93 c1 00 08 stw r30,8(r1)
138: 7f c8 02 a6 mflr r30
13c: 3f de 00 00 addis r30,r30,0
13e: R_PPC_REL16_HA .got2+0x8012
140: 90 01 00 14 stw r0,20(r1)
144: 3b de 00 00 addi r30,r30,0
146: R_PPC_REL16_LO .got2+0x801a
148: 81 5e 80 00 lwz r10,-32768(r30)
14c: 80 fe 80 04 lwz r7,-32764(r30)
Also declare longjmp() and start_secondary_resume() as global noreturn
functions, and declare __copy_tofrom_user() and __arch_clear_user()
as UACCESS safe.
Signed-off-by: Christophe Leroy <christophe.leroy@xxxxxxxxxx>
---
arch/powerpc/Kconfig | 2 +
arch/powerpc/include/asm/kup.h | 12 +++
arch/powerpc/include/asm/nohash/32/kup-8xx.h | 8 +-
arch/powerpc/include/asm/nohash/kup-booke.h | 8 +-
arch/powerpc/kexec/core_32.c | 4 +-
tools/objtool/arch/powerpc/decode.c | 83 +++++++++++++++++--
.../arch/powerpc/include/arch/noreturns.h | 11 +++
tools/objtool/arch/powerpc/special.c | 34 +++++++-
tools/objtool/check.c | 6 +-
9 files changed, 152 insertions(+), 16 deletions(-)
create mode 100644 tools/objtool/arch/powerpc/include/arch/noreturns.h
diff --git a/arch/powerpc/Kconfig b/arch/powerpc/Kconfig
index 8b955bc7b59f..8b613e520143 100644
--- a/arch/powerpc/Kconfig
+++ b/arch/powerpc/Kconfig
@@ -160,6 +160,7 @@ config PPC
select ARCH_KEEP_MEMBLOCK
select ARCH_MIGHT_HAVE_PC_PARPORT
select ARCH_MIGHT_HAVE_PC_SERIO
+ select ARCH_OBJTOOL_SKIP_ASM
select ARCH_OPTIONAL_KERNEL_RWX if ARCH_HAS_STRICT_KERNEL_RWX
select ARCH_OPTIONAL_KERNEL_RWX_DEFAULT
select ARCH_SPLIT_ARG64 if PPC32
@@ -258,6 +259,7 @@ config PPC
select HAVE_OPTPROBES
select HAVE_OBJTOOL if PPC32 || MPROFILE_KERNEL
select HAVE_OBJTOOL_MCOUNT if HAVE_OBJTOOL
+ select HAVE_UACCESS_VALIDATION if HAVE_OBJTOOL && PPC_KUAP && PPC32
select HAVE_PERF_EVENTS
select HAVE_PERF_EVENTS_NMI if PPC64
select HAVE_PERF_REGS
diff --git a/arch/powerpc/include/asm/kup.h b/arch/powerpc/include/asm/kup.h
index 132f1c7e1064..9f824cb93d8a 100644
--- a/arch/powerpc/include/asm/kup.h
+++ b/arch/powerpc/include/asm/kup.h
@@ -10,6 +10,8 @@
#include <linux/types.h>
static __always_inline bool kuap_is_disabled(void);
+static __always_inline void mtspr_uaccess_begin(int rn, unsigned long val);
+static __always_inline void mtspr_uaccess_end(int rn, unsigned long val);
#endif
#ifdef CONFIG_PPC_BOOK3S_64
@@ -222,6 +224,16 @@ static __always_inline void prevent_current_write_to_user(void)
prevent_user_access(KUAP_WRITE);
}
+static __always_inline void mtspr_uaccess_begin(int rn, unsigned long val)
+{
+ asm(ASM_UACCESS_BEGIN "mtspr %0, %1\n\t" : : "i"(rn), "r"(val) : "memory");
+}
+
+static __always_inline void mtspr_uaccess_end(int rn, unsigned long val)
+{
+ asm(ASM_UACCESS_END "mtspr %0, %1\n\t" : : "i"(rn), "r"(val) : "memory");
+}
+
#endif /* !__ASSEMBLY__ */
#endif /* _ASM_POWERPC_KUAP_H_ */
diff --git a/arch/powerpc/include/asm/nohash/32/kup-8xx.h b/arch/powerpc/include/asm/nohash/32/kup-8xx.h
index 61067e4c8f22..9b59231d87c9 100644
--- a/arch/powerpc/include/asm/nohash/32/kup-8xx.h
+++ b/arch/powerpc/include/asm/nohash/32/kup-8xx.h
@@ -42,12 +42,12 @@ static __always_inline unsigned long __kuap_get_and_assert_locked(void)
static __always_inline void __allow_user_access(void __user *to, const void __user *from,
unsigned long size, unsigned long dir)
{
- mtspr(SPRN_MD_AP, MD_APG_INIT);
+ mtspr_uaccess_begin(SPRN_MD_AP, MD_APG_INIT);
}
static __always_inline void __prevent_user_access(unsigned long dir)
{
- mtspr(SPRN_MD_AP, MD_APG_KUAP);
+ mtspr_uaccess_end(SPRN_MD_AP, MD_APG_KUAP);
}
static __always_inline unsigned long __prevent_user_access_return(void)
@@ -56,14 +56,14 @@ static __always_inline unsigned long __prevent_user_access_return(void)
flags = mfspr(SPRN_MD_AP);
- mtspr(SPRN_MD_AP, MD_APG_KUAP);
+ mtspr_uaccess_end(SPRN_MD_AP, MD_APG_KUAP);
return flags;
}
static __always_inline void __restore_user_access(unsigned long flags)
{
- mtspr(SPRN_MD_AP, flags);
+ mtspr_uaccess_begin(SPRN_MD_AP, flags);
}
static __always_inline bool
diff --git a/arch/powerpc/include/asm/nohash/kup-booke.h b/arch/powerpc/include/asm/nohash/kup-booke.h
index 416f3e0897d5..2967501c434e 100644
--- a/arch/powerpc/include/asm/nohash/kup-booke.h
+++ b/arch/powerpc/include/asm/nohash/kup-booke.h
@@ -64,13 +64,13 @@ static __always_inline unsigned long __kuap_get_and_assert_locked(void)
static __always_inline void __allow_user_access(void __user *to, const void __user *from,
unsigned long size, unsigned long dir)
{
- mtspr(SPRN_PID, current->thread.pid);
+ mtspr_uaccess_begin(SPRN_PID, current->thread.pid);
isync();
}
static __always_inline void __prevent_user_access(unsigned long dir)
{
- mtspr(SPRN_PID, 0);
+ mtspr_uaccess_end(SPRN_PID, 0);
isync();
}
@@ -78,7 +78,7 @@ static __always_inline unsigned long __prevent_user_access_return(void)
{
unsigned long flags = mfspr(SPRN_PID);
- mtspr(SPRN_PID, 0);
+ mtspr_uaccess_end(SPRN_PID, 0);
isync();
return flags;
@@ -87,7 +87,7 @@ static __always_inline unsigned long __prevent_user_access_return(void)
static __always_inline void __restore_user_access(unsigned long flags)
{
if (flags) {
- mtspr(SPRN_PID, current->thread.pid);
+ mtspr_uaccess_begin(SPRN_PID, current->thread.pid);
isync();
}
}
diff --git a/arch/powerpc/kexec/core_32.c b/arch/powerpc/kexec/core_32.c
index c95f96850c9e..6e955f32e7c3 100644
--- a/arch/powerpc/kexec/core_32.c
+++ b/arch/powerpc/kexec/core_32.c
@@ -17,7 +17,7 @@
typedef void (*relocate_new_kernel_t)(
unsigned long indirection_page,
unsigned long reboot_code_buffer,
- unsigned long start_address) __noreturn;
+ unsigned long start_address);
/*
* This is a generic machine_kexec function suitable at least for
@@ -61,6 +61,8 @@ void default_machine_kexec(struct kimage *image)
/* now call it */
rnk = (relocate_new_kernel_t) reboot_code_buffer;
(*rnk)(page_list, reboot_code_buffer_phys, image->start);
+
+ unreachable(); /* For objtool */
}
int machine_kexec_prepare(struct kimage *image)
diff --git a/tools/objtool/arch/powerpc/decode.c b/tools/objtool/arch/powerpc/decode.c
index 53b55690f320..bac861cf1176 100644
--- a/tools/objtool/arch/powerpc/decode.c
+++ b/tools/objtool/arch/powerpc/decode.c
@@ -43,24 +43,95 @@ int arch_decode_instruction(struct objtool_file *file, const struct section *sec
unsigned long offset, unsigned int maxlen,
struct instruction *insn)
{
- unsigned int opcode;
+ unsigned int opcode, xop;
+ unsigned int rs, ra, rb, bo, bi, to, uimm, simm, lk, aa;
enum insn_type typ;
unsigned long imm;
u32 ins;
ins = bswap_if_needed(file->elf, *(u32 *)(sec->data->d_buf + offset));
+
+ if (!ins && file->elf->ehdr.e_flags & EF_PPC_RELOCATABLE_LIB) {
+ struct reloc *reloc;
+
+ reloc = find_reloc_by_dest_range(file->elf, insn->sec, insn->offset, 4);
+
+ if (reloc && reloc_type(reloc) == R_PPC_REL32 &&
+ !strncmp(reloc->sym->sec->name, ".got2", 5)) {
+ insn->type = INSN_OTHER;
+ insn->ignore = true;
+ insn->len = 4;
+
+ return 0;
+ }
+ }
+
opcode = ins >> 26;
- typ = INSN_OTHER;
- imm = 0;
+ xop = (ins >> 1) & 0x3ff;
+ rs = bo = to = (ins >> 21) & 0x1f;
+ ra = bi = (ins >> 16) & 0x1f;
+ rb = (ins >> 11) & 0x1f;
+ uimm = simm = (ins >> 0) & 0xffff;
+ aa = ins & 2;
+ lk = ins & 1;
switch (opcode) {
+ case 3:
+ if (to == 31 && ra == 0 && simm == 0) /* twi 31, r0, 0 */
+ typ = INSN_BUG;
+ else
+ typ = INSN_OTHER;
+ break;
+ case 16: /* bc[l][a] */
+ if (lk) /* bcl[a] */
+ typ = INSN_OTHER;
+ else /* bc[a] */
+ typ = INSN_JUMP_CONDITIONAL;
+
+ imm = ins & 0xfffc;
+ if (imm & 0x8000)
+ imm -= 0x10000;
+ insn->immediate = imm | aa;
+ break;
case 18: /* b[l][a] */
- if ((ins & 3) == 1) /* bl */
+ if (lk) /* bl[a] */
typ = INSN_CALL;
+ else /* b[a] */
+ typ = INSN_JUMP_UNCONDITIONAL;
imm = ins & 0x3fffffc;
if (imm & 0x2000000)
imm -= 0x4000000;
+ insn->immediate = imm | aa;
+ break;
+ case 19:
+ if (xop == 16 && bo == 20 && bi == 0) /* blr */
+ typ = INSN_RETURN;
+ else if (xop == 16) /* bclr */
+ typ = INSN_RETURN_CONDITIONAL;
+ else if (xop == 50) /* rfi */
+ typ = INSN_JUMP_DYNAMIC;
+ else if (xop == 528 && bo == 20 && bi == 0 && !lk) /* bctr */
+ typ = INSN_JUMP_DYNAMIC;
+ else if (xop == 528 && bo == 20 && bi == 0 && lk) /* bctrl */
+ typ = INSN_CALL_DYNAMIC;
+ else
+ typ = INSN_OTHER;
+ break;
+ case 24:
+ if (rs == 0 && ra == 0 && uimm == 0)
+ typ = INSN_NOP;
+ else
+ typ = INSN_OTHER;
+ break;
+ case 31:
+ if (xop == 4 && to == 31 && ra == 0 && rb == 0) /* trap */
+ typ = INSN_BUG;
+ else
+ typ = INSN_OTHER;
+ break;
+ default:
+ typ = INSN_OTHER;
break;
}
@@ -70,13 +141,15 @@ int arch_decode_instruction(struct objtool_file *file, const struct section *sec
insn->len = 4;
insn->type = typ;
- insn->immediate = imm;
return 0;
}
unsigned long arch_jump_destination(struct instruction *insn)
{
+ if (insn->immediate & 2)
+ return insn->immediate & ~2;
+
return insn->offset + insn->immediate;
}
diff --git a/tools/objtool/arch/powerpc/include/arch/noreturns.h b/tools/objtool/arch/powerpc/include/arch/noreturns.h
new file mode 100644
index 000000000000..664f17d39026
--- /dev/null
+++ b/tools/objtool/arch/powerpc/include/arch/noreturns.h
@@ -0,0 +1,11 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+
+/*
+ * This is a (sorted!) list of all known __noreturn functions in arch/powerpc.
+ * It's needed for objtool to properly reverse-engineer the control flow graph.
+ *
+ * Yes, this is unfortunate. A better solution is in the works.
+ */
+NORETURN(longjmp)
+NORETURN(start_secondary_resume)
+NORETURN(unrecoverable_exception)
diff --git a/tools/objtool/arch/powerpc/special.c b/tools/objtool/arch/powerpc/special.c
index d33868147196..21940cbfd550 100644
--- a/tools/objtool/arch/powerpc/special.c
+++ b/tools/objtool/arch/powerpc/special.c
@@ -15,5 +15,37 @@ bool arch_support_alt_relocation(struct special_alt *special_alt,
struct reloc *arch_find_switch_table(struct objtool_file *file,
struct instruction *insn)
{
- exit(-1);
+ struct reloc *text_reloc;
+ struct section *table_sec;
+ unsigned long table_offset;
+
+ /* look for a relocation which references .rodata */
+ text_reloc = find_reloc_by_dest_range(file->elf, insn->sec,
+ insn->offset, insn->len);
+ if (!text_reloc || text_reloc->sym->type != STT_SECTION ||
+ !text_reloc->sym->sec->rodata)
+ return NULL;
+
+ table_offset = reloc_addend(text_reloc);
+ table_sec = text_reloc->sym->sec;
+
+ /*
+ * Make sure the .rodata address isn't associated with a
+ * symbol. GCC jump tables are anonymous data.
+ *
+ * Also support C jump tables which are in the same format as
+ * switch jump tables. For objtool to recognize them, they
+ * need to be placed in the C_JUMP_TABLE_SECTION section. They
+ * have symbols associated with them.
+ */
+ if (find_symbol_containing(table_sec, table_offset) &&
+ strcmp(table_sec->name, C_JUMP_TABLE_SECTION))
+ return NULL;
+
+ /*
+ * Each table entry has a rela associated with it. The rela
+ * should reference text in the same function as the original
+ * instruction.
+ */
+ return find_reloc_by_dest(file->elf, table_sec, table_offset);
}
diff --git a/tools/objtool/check.c b/tools/objtool/check.c
index 6daa13c25183..2d564d0e2ae1 100644
--- a/tools/objtool/check.c
+++ b/tools/objtool/check.c
@@ -1259,13 +1259,17 @@ static const char *uaccess_safe_builtin[] = {
"stackleak_track_stack",
/* misc */
"csum_partial_copy_generic",
+ "ftrace_likely_update", /* CONFIG_TRACE_BRANCH_PROFILING */
+ /* misc x86 */
"copy_mc_fragile",
"copy_mc_fragile_handle_tail",
"copy_mc_enhanced_fast_string",
- "ftrace_likely_update", /* CONFIG_TRACE_BRANCH_PROFILING */
"rep_stos_alternative",
"rep_movs_alternative",
"__copy_user_nocache",
+ /* misc powerpc */
+ "__copy_tofrom_user",
+ "__arch_clear_user",
NULL
};
--
2.40.1