Message-Id: <be282f27ad808418c7475b51a00b4cb035f89a95.1687430631.git.christophe.leroy@csgroup.eu>
Date:   Thu, 22 Jun 2023 12:54:36 +0200
From:   Christophe Leroy <christophe.leroy@...roup.eu>
To:     Michael Ellerman <mpe@...erman.id.au>,
        Nicholas Piggin <npiggin@...il.com>,
        Josh Poimboeuf <jpoimboe@...nel.org>,
        Peter Zijlstra <peterz@...radead.org>,
        Sathvika Vasireddy <sv@...ux.ibm.com>,
        Naveen N Rao <naveen@...nel.org>
Cc:     Christophe Leroy <christophe.leroy@...roup.eu>,
        linux-kernel@...r.kernel.org, linuxppc-dev@...ts.ozlabs.org
Subject: [PATCH v2 14/14] powerpc: Implement UACCESS validation on PPC32

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: 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@...roup.eu>
---
 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          | 82 ++++++++++++++++++--
 tools/objtool/arch/powerpc/special.c         | 42 +++++++++-
 tools/objtool/check.c                        |  5 ++
 8 files changed, 148 insertions(+), 15 deletions(-)

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..2ed5241eb7be 100644
--- a/tools/objtool/arch/powerpc/decode.c
+++ b/tools/objtool/arch/powerpc/decode.c
@@ -43,24 +43,94 @@ 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;
 
+	if (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 == R_PPC_REL32 &&
+		    !strncmp(reloc->sym->sec->name, ".got2", 5)) {
+			insn->type = INSN_OTHER;
+			insn->ignore = true;
+			insn->len = 4;
+
+			return 0;
+		}
+	}
+
 	ins = bswap_if_needed(file->elf, *(u32 *)(sec->data->d_buf + offset));
 	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 +140,15 @@ 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/special.c b/tools/objtool/arch/powerpc/special.c
index 979b555b16ea..be37f4b455dc 100644
--- a/tools/objtool/arch/powerpc/special.c
+++ b/tools/objtool/arch/powerpc/special.c
@@ -15,5 +15,45 @@ bool arch_support_alt_relocation(struct special_alt *special_alt,
 struct reloc *arch_find_switch_table(struct objtool_file *file,
 				     struct instruction *insn, bool *is_rel)
 {
-	exit(-1);
+	struct reloc  *text_reloc, *rodata_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 = text_reloc->addend;
+	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)) {
+		if (strcmp(table_sec->name, C_JUMP_TABLE_SECTION))
+			return NULL;
+		*is_rel = false;
+	} else {
+		*is_rel = true;
+	}
+
+	/*
+	 * Each table entry has a rela associated with it.  The rela
+	 * should reference text in the same function as the original
+	 * instruction.
+	 */
+	rodata_reloc = find_reloc_by_dest(file->elf, table_sec, table_offset);
+	if (!rodata_reloc)
+		return NULL;
+
+	return rodata_reloc;
 }
diff --git a/tools/objtool/check.c b/tools/objtool/check.c
index f850ab892ad5..8ac5711a055f 100644
--- a/tools/objtool/check.c
+++ b/tools/objtool/check.c
@@ -218,6 +218,7 @@ static bool __dead_end_function(struct objtool_file *file, struct symbol *func,
 		"kthread_exit",
 		"kunit_try_catch_throw",
 		"lbug_with_loc",
+		"longjmp",
 		"machine_real_restart",
 		"make_task_dead",
 		"mpt_halt_firmware",
@@ -230,7 +231,9 @@ static bool __dead_end_function(struct objtool_file *file, struct symbol *func,
 		"sev_es_terminate",
 		"snp_abort",
 		"start_kernel",
+		"start_secondary_resume",
 		"stop_this_cpu",
+		"unrecoverable_exception",
 		"usercopy_abort",
 		"x86_64_start_kernel",
 		"x86_64_start_reservations",
@@ -1335,6 +1338,8 @@ static const char *uaccess_safe_builtin[] = {
 	"rep_stos_alternative",
 	"rep_movs_alternative",
 	"__copy_user_nocache",
+	"__copy_tofrom_user",
+	"__arch_clear_user",
 	NULL
 };
 
-- 
2.40.1

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