Re: [PATCH] binfmt_elf_fdpic: fix /proc/<pid>/auxv

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Hi Max,

On 23/3/24 05:54, Max Filippov wrote:
Althought FDPIC linux kernel provides /proc/<pid>/auxv files they are
empty because there's no code that initializes mm->saved_auxv in the
FDPIC ELF loader.

Synchronize FDPIC ELF aux vector setup with ELF. Replace entry-by-entry
aux vector copying to userspace with initialization of mm->saved_auxv
first and then copying it to userspace as a whole.

Signed-off-by: Max Filippov <jcmvbkbc@xxxxxxxxx>

This is breaking ARM nommu builds supporting fdpic and elf binaries for me.

Tests I have for m68k and riscv nommu setups running elf binaries
don't show any problems - I am only seeing this on ARM.


...
Freeing unused kernel image (initmem) memory: 472K
This architecture does not have kernel memory protection.
Run /init as init process
Internal error: Oops - undefined instruction: 0 [#1] ARM
Modules linked in:
CPU: 0 PID: 1 Comm: init Not tainted 6.10.0 #1
Hardware name: ARM-Versatile (Device Tree Support)
PC is at load_elf_fdpic_binary+0xb34/0xb80
LR is at 0x0
pc : [<00109ce8>]    lr : [<00000000>]    psr: 80000153
sp : 00823e40  ip : 00000000  fp : 00b8fee4
r10: 009c9b80  r9 : 00b8ff80  r8 : 009ee800
r7 : 00000000  r6 : 009f7e80  r5 : 00b8fedc  r4 : 00b87000
r3 : 00b8fed8  r2 : 00b8fee0  r1 : 00b87128  r0 : 00b8fef0
Flags: Nzcv  IRQs on  FIQs off  Mode SVC_32  ISA ARM  Segment none
Control: 00091176  Table: 00000000  DAC: 00000000
Register r0 information: non-slab/vmalloc memory
Register r1 information: slab/vmalloc mm_struct start 00b87000 pointer offset 296 size 428
Register r2 information: non-slab/vmalloc memory
Register r3 information: non-slab/vmalloc memory
Register r4 information: slab/vmalloc mm_struct start 00b87000 pointer offset 0 size 428
Register r5 information: non-slab/vmalloc memory
Register r6 information: slab/vmalloc kmalloc-32 start 009f7e80 pointer offset 0 size 32
Register r7 information: non-slab/vmalloc memory
Register r8 information: slab/vmalloc kmalloc-512 start 009ee800 pointer offset 0 size 512
Register r9 information: non-slab/vmalloc memory
Register r10 information: slab/vmalloc kmalloc-128 start 009c9b80 pointer offset 0 size 128
Register r11 information: non-slab/vmalloc memory
Register r12 information: non-slab/vmalloc memory
Process init (pid: 1, stack limit = 0x(ptrval))
Stack: (0x00823e40 to 0x00824000)
3e40: ???????? ???????? ???????? ???????? ???????? ???????? ???????? ????????
3e60: ???????? ???????? ???????? ???????? ???????? ???????? ???????? ????????
3e80: ???????? ???????? ???????? ???????? ???????? ???????? ???????? ????????
3ea0: ???????? ???????? ???????? ???????? ???????? ???????? ???????? ????????
3ec0: ???????? ???????? ???????? ???????? ???????? ???????? ???????? ????????
3ee0: ???????? ???????? ???????? ???????? ???????? ???????? ???????? ????????
3f00: ???????? ???????? ???????? ???????? ???????? ???????? ???????? ????????
3f20: ???????? ???????? ???????? ???????? ???????? ???????? ???????? ????????
3f40: ???????? ???????? ???????? ???????? ???????? ???????? ???????? ????????
3f60: ???????? ???????? ???????? ???????? ???????? ???????? ???????? ????????
3f80: ???????? ???????? ???????? ???????? ???????? ???????? ???????? ????????
3fa0: ???????? ???????? ???????? ???????? ???????? ???????? ???????? ????????
3fc0: ???????? ???????? ???????? ???????? ???????? ???????? ???????? ????????
3fe0: ???????? ???????? ???????? ???????? ???????? ???????? ???????? ????????
Call trace:
 load_elf_fdpic_binary from bprm_execve+0x1b4/0x488
 bprm_execve from kernel_execve+0x154/0x1e4
 kernel_execve from kernel_init+0x4c/0x108
 kernel_init from ret_from_fork+0x14/0x38
Exception stack(0x00823fb0 to 0x00823ff8)
3fa0:                                     ???????? ???????? ???????? ????????
3fc0: ???????? ???????? ???????? ???????? ???????? ???????? ???????? ????????
3fe0: ???????? ???????? ???????? ???????? ???????? ????????
Code: bad PC value
---[ end trace 0000000000000000 ]---
note: init[1] exited with irqs disabled
Kernel panic - not syncing: Attempted to kill init! exitcode=0x0000000b
---[ end Kernel panic - not syncing: Attempted to kill init! exitcode=0x0000000b ]---


The code around that PC is:

  109cd0:       e2833ff1        add     r3, r3, #964    @ 0x3c4
  109cd4:       e5933000        ldr     r3, [r3]
  109cd8:       e5933328        ldr     r3, [r3, #808]  @ 0x328
  109cdc:       e5933084        ldr     r3, [r3, #132]  @ 0x84
  109ce0:       e5843034        str     r3, [r4, #52]   @ 0x34
  109ce4:       eafffdbc        b       1093dc <load_elf_fdpic_binary+0x228>
  109ce8:       e7f001f2        .word   0xe7f001f2
  109cec:       eb09471d        bl      35b968 <__stack_chk_fail>
  109cf0:       e59f0038        ldr     r0, [pc, #56]   @ 109d30 <load_elf_fdpic_binary+0xb7c>
  109cf4:       eb092f03        bl      355908 <_printk>
  109cf8:       eafffdb7        b       1093dc <load_elf_fdpic_binary+0x228>


Reverting just this change gets it working again.

Any idea what might be going on?

Regards
Greg


---
  fs/binfmt_elf_fdpic.c | 88 +++++++++++++++++++++----------------------
  1 file changed, 42 insertions(+), 46 deletions(-)

diff --git a/fs/binfmt_elf_fdpic.c b/fs/binfmt_elf_fdpic.c
index fefc642541cb..7b4542a0cbe3 100644
--- a/fs/binfmt_elf_fdpic.c
+++ b/fs/binfmt_elf_fdpic.c
@@ -505,8 +505,9 @@ static int create_elf_fdpic_tables(struct linux_binprm *bprm,
  	char *k_platform, *k_base_platform;
  	char __user *u_platform, *u_base_platform, *p;
  	int loop;
-	int nr;	/* reset for each csp adjustment */
  	unsigned long flags = 0;
+	int ei_index;
+	elf_addr_t *elf_info;
#ifdef CONFIG_MMU
  	/* In some cases (e.g. Hyper-Threading), we want to avoid L1 evictions
@@ -601,44 +602,24 @@ static int create_elf_fdpic_tables(struct linux_binprm *bprm,
  	csp -= sp & 15UL;
  	sp -= sp & 15UL;
- /* put the ELF interpreter info on the stack */
-#define NEW_AUX_ENT(id, val)						\
-	do {								\
-		struct { unsigned long _id, _val; } __user *ent, v;	\
-									\
-		ent = (void __user *) csp;				\
-		v._id = (id);						\
-		v._val = (val);						\
-		if (copy_to_user(ent + nr, &v, sizeof(v)))		\
-			return -EFAULT;					\
-		nr++;							\
+	/* Create the ELF interpreter info */
+	elf_info = (elf_addr_t *)mm->saved_auxv;
+	/* update AT_VECTOR_SIZE_BASE if the number of NEW_AUX_ENT() changes */
+#define NEW_AUX_ENT(id, val) \
+	do { \
+		*elf_info++ = id; \
+		*elf_info++ = val; \
  	} while (0)
- nr = 0;
-	csp -= 2 * sizeof(unsigned long);
-	NEW_AUX_ENT(AT_NULL, 0);
-	if (k_platform) {
-		nr = 0;
-		csp -= 2 * sizeof(unsigned long);
-		NEW_AUX_ENT(AT_PLATFORM,
-			    (elf_addr_t) (unsigned long) u_platform);
-	}
-
-	if (k_base_platform) {
-		nr = 0;
-		csp -= 2 * sizeof(unsigned long);
-		NEW_AUX_ENT(AT_BASE_PLATFORM,
-			    (elf_addr_t) (unsigned long) u_base_platform);
-	}
-
-	if (bprm->have_execfd) {
-		nr = 0;
-		csp -= 2 * sizeof(unsigned long);
-		NEW_AUX_ENT(AT_EXECFD, bprm->execfd);
-	}
-
-	nr = 0;
-	csp -= DLINFO_ITEMS * 2 * sizeof(unsigned long);
+#ifdef ARCH_DLINFO
+	/*
+	 * ARCH_DLINFO must come first so PPC can do its special alignment of
+	 * AUXV.
+	 * update AT_VECTOR_SIZE_ARCH if the number of NEW_AUX_ENT() in
+	 * ARCH_DLINFO changes
+	 */
+	ARCH_DLINFO;
+#endif
  	NEW_AUX_ENT(AT_HWCAP,	ELF_HWCAP);
  #ifdef ELF_HWCAP2
  	NEW_AUX_ENT(AT_HWCAP2,	ELF_HWCAP2);
@@ -659,17 +640,32 @@ static int create_elf_fdpic_tables(struct linux_binprm *bprm,
  	NEW_AUX_ENT(AT_EGID,	(elf_addr_t) from_kgid_munged(cred->user_ns, cred->egid));
  	NEW_AUX_ENT(AT_SECURE,	bprm->secureexec);
  	NEW_AUX_ENT(AT_EXECFN,	bprm->exec);
+	if (k_platform) {
+		NEW_AUX_ENT(AT_PLATFORM,
+			    (elf_addr_t)(unsigned long)u_platform);
+	}
+	if (k_base_platform) {
+		NEW_AUX_ENT(AT_BASE_PLATFORM,
+			    (elf_addr_t)(unsigned long)u_base_platform);
+	}
+	if (bprm->have_execfd) {
+		NEW_AUX_ENT(AT_EXECFD, bprm->execfd);
+	}
+#undef NEW_AUX_ENT
+	/* AT_NULL is zero; clear the rest too */
+	memset(elf_info, 0, (char *)mm->saved_auxv +
+	       sizeof(mm->saved_auxv) - (char *)elf_info);
-#ifdef ARCH_DLINFO
-	nr = 0;
-	csp -= AT_VECTOR_SIZE_ARCH * 2 * sizeof(unsigned long);
+	/* And advance past the AT_NULL entry.  */
+	elf_info += 2;
- /* ARCH_DLINFO must come last so platform specific code can enforce
-	 * special alignment requirements on the AUXV if necessary (eg. PPC).
-	 */
-	ARCH_DLINFO;
-#endif
-#undef NEW_AUX_ENT
+	ei_index = elf_info - (elf_addr_t *)mm->saved_auxv;
+	csp -= ei_index * sizeof(elf_addr_t);
+
+	/* Put the elf_info on the stack in the right place.  */
+	if (copy_to_user((void __user *)csp, mm->saved_auxv,
+			 ei_index * sizeof(elf_addr_t)))
+		return -EFAULT;
/* allocate room for argv[] and envv[] */
  	csp -= (bprm->envc + 1) * sizeof(elf_caddr_t);




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