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[Qemu-devel] [PATCH] linux-user: remove MAX_ARG_PAGES, allow dynamic gro


From: Stefan Brüns
Subject: [Qemu-devel] [PATCH] linux-user: remove MAX_ARG_PAGES, allow dynamic growth of env/argv space
Date: Sat, 15 Aug 2015 20:26:01 +0200

qemu currently limits the space for the evironment and arguments to
32 * PAGE_SIZE. Linux limits the argument space to 1/4 of the stack size.
A program trying to detect this with a getrlimit(RLIMIT_STACK) syscall
will typically get a much larger limit than qemus current 128kB.

The current limit causes "Argument list too long" errors.

Signed-off-by: Stefan Brüns <address@hidden>
---
 linux-user/elfload.c   | 29 ++++++++++++++++++-----------
 linux-user/linuxload.c |  7 ++++---
 linux-user/qemu.h      | 11 ++---------
 linux-user/syscall.c   |  4 ++++
 4 files changed, 28 insertions(+), 23 deletions(-)

diff --git a/linux-user/elfload.c b/linux-user/elfload.c
index 1788368..be8f4d6 100644
--- a/linux-user/elfload.c
+++ b/linux-user/elfload.c
@@ -1365,11 +1365,13 @@ static bool elf_check_ehdr(struct elfhdr *ehdr)
  * to be put directly into the top of new user memory.
  *
  */
-static abi_ulong copy_elf_strings(int argc,char ** argv, void **page,
-                                  abi_ulong p)
+static abi_ulong copy_elf_strings(int argc,char ** argv,
+                                  struct linux_binprm *bprm)
 {
     char *tmp, *tmp1, *pag = NULL;
     int len, offset = 0;
+    void **page = bprm->page;
+    abi_ulong p = bprm->p;
 
     if (!p) {
         return 0;       /* bullet-proofing */
@@ -1383,8 +1385,13 @@ static abi_ulong copy_elf_strings(int argc,char ** argv, 
void **page,
         tmp1 = tmp;
         while (*tmp++);
         len = tmp - tmp1;
-        if (p < len) {  /* this shouldn't happen - 128kB */
-            return 0;
+        if (p < len) {
+            bprm->page = (void**)calloc(bprm->n_arg_pages + 32, sizeof(void*));
+            memcpy(&bprm->page[32], page, sizeof(void*) * bprm->n_arg_pages);
+            free(page);
+            page = bprm->page;
+            bprm->n_arg_pages += 32;
+            p += 32 * TARGET_PAGE_SIZE;
         }
         while (len) {
             --p; --tmp; --len;
@@ -1423,8 +1430,8 @@ static abi_ulong setup_arg_pages(abi_ulong p, struct 
linux_binprm *bprm,
     /* Create enough stack to hold everything.  If we don't use
        it for args, we'll use it for something else.  */
     size = guest_stack_size;
-    if (size < MAX_ARG_PAGES*TARGET_PAGE_SIZE) {
-        size = MAX_ARG_PAGES*TARGET_PAGE_SIZE;
+    if (size < bprm->n_arg_pages * TARGET_PAGE_SIZE) {
+        size = bprm->n_arg_pages * TARGET_PAGE_SIZE;
     }
     guard = TARGET_PAGE_SIZE;
     if (guard < qemu_real_host_page_size) {
@@ -1442,10 +1449,10 @@ static abi_ulong setup_arg_pages(abi_ulong p, struct 
linux_binprm *bprm,
     target_mprotect(error, guard, PROT_NONE);
 
     info->stack_limit = error + guard;
-    stack_base = info->stack_limit + size - MAX_ARG_PAGES*TARGET_PAGE_SIZE;
+    stack_base = info->stack_limit + size - bprm->n_arg_pages * 
TARGET_PAGE_SIZE;
     p += stack_base;
 
-    for (i = 0 ; i < MAX_ARG_PAGES ; i++) {
+    for (i = 0; i < bprm->n_arg_pages; i++) {
         if (bprm->page[i]) {
             info->rss++;
             /* FIXME - check return value of memcpy_to_target() for failure */
@@ -2211,9 +2218,9 @@ int load_elf_binary(struct linux_binprm *bprm, struct 
image_info *info)
        when we load the interpreter.  */
     elf_ex = *(struct elfhdr *)bprm->buf;
 
-    bprm->p = copy_elf_strings(1, &bprm->filename, bprm->page, bprm->p);
-    bprm->p = copy_elf_strings(bprm->envc,bprm->envp,bprm->page,bprm->p);
-    bprm->p = copy_elf_strings(bprm->argc,bprm->argv,bprm->page,bprm->p);
+    bprm->p = copy_elf_strings(1, &bprm->filename, bprm);
+    bprm->p = copy_elf_strings(bprm->envc, bprm->envp, bprm);
+    bprm->p = copy_elf_strings(bprm->argc, bprm->argv, bprm);
     if (!bprm->p) {
         fprintf(stderr, "%s: %s\n", bprm->filename, strerror(E2BIG));
         exit(-1);
diff --git a/linux-user/linuxload.c b/linux-user/linuxload.c
index 506e837..59943ea 100644
--- a/linux-user/linuxload.c
+++ b/linux-user/linuxload.c
@@ -137,8 +137,9 @@ int loader_exec(int fdexec, const char *filename, char 
**argv, char **envp,
     int retval;
     int i;
 
-    bprm->p = TARGET_PAGE_SIZE*MAX_ARG_PAGES-sizeof(unsigned int);
-    memset(bprm->page, 0, sizeof(bprm->page));
+    bprm->n_arg_pages = 32;
+    bprm->p = bprm->n_arg_pages * TARGET_PAGE_SIZE - sizeof(unsigned int);
+    bprm->page = (void**)calloc(bprm->n_arg_pages, sizeof(void*));
     bprm->fd = fdexec;
     bprm->filename = (char *)filename;
     bprm->argc = count(argv);
@@ -173,7 +174,7 @@ int loader_exec(int fdexec, const char *filename, char 
**argv, char **envp,
     }
 
     /* Something went wrong, return the inode and free the argument pages*/
-    for (i=0 ; i<MAX_ARG_PAGES ; i++) {
+    for (i = 0; i < bprm->n_arg_pages; i++) {
         g_free(bprm->page[i]);
     }
     return(retval);
diff --git a/linux-user/qemu.h b/linux-user/qemu.h
index 8012cc2..cf4aa73 100644
--- a/linux-user/qemu.h
+++ b/linux-user/qemu.h
@@ -144,14 +144,6 @@ void stop_all_tasks(void);
 extern const char *qemu_uname_release;
 extern unsigned long mmap_min_addr;
 
-/* ??? See if we can avoid exposing so much of the loader internals.  */
-/*
- * MAX_ARG_PAGES defines the number of pages allocated for arguments
- * and envelope for the new program. 32 should suffice, this gives
- * a maximum env+arg of 128kB w/4KB pages!
- */
-#define MAX_ARG_PAGES 33
-
 /* Read a good amount of data initially, to hopefully get all the
    program headers loaded.  */
 #define BPRM_BUF_SIZE  1024
@@ -162,7 +154,8 @@ extern unsigned long mmap_min_addr;
  */
 struct linux_binprm {
         char buf[BPRM_BUF_SIZE] __attribute__((aligned));
-        void *page[MAX_ARG_PAGES];
+        void **page;
+        int n_arg_pages;
         abi_ulong p;
        int fd;
         int e_uid, e_gid;
diff --git a/linux-user/syscall.c b/linux-user/syscall.c
index f62c698..6fa5fb4 100644
--- a/linux-user/syscall.c
+++ b/linux-user/syscall.c
@@ -5799,12 +5799,16 @@ abi_long do_syscall(void *cpu_env, int num, abi_long 
arg1,
             }
             *q = NULL;
 
+/* This check is bogus. MAX_ARG_PAGES is a thing of the past. Trust the host
+execve to set errno appropriately */
+#if 0
             /* This case will not be caught by the host's execve() if its
                page size is bigger than the target's. */
             if (total_size > MAX_ARG_PAGES * TARGET_PAGE_SIZE) {
                 ret = -TARGET_E2BIG;
                 goto execve_end;
             }
+#endif
             if (!(p = lock_user_string(arg1)))
                 goto execve_efault;
             ret = get_errno(execve(p, argp, envp));
-- 
2.1.4




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