ELF loader support for auxvec base platform string
Some IBM POWER-based platforms have the ability to run in a
mode which mostly appears to the OS as a different processor from the
actual hardware. For example, a Power6 system may appear to be a
Power5+, which makes the AT_PLATFORM value "power5+". This means that
programs are restricted to the ISA supported by Power5+;
Power6-specific instructions are treated as illegal.
However, some applications (virtual machines, optimized libraries) can
benefit from knowledge of the underlying CPU model. A new aux vector
entry, AT_BASE_PLATFORM, will denote the actual hardware. For
example, on a Power6 system in Power5+ compatibility mode, AT_PLATFORM
will be "power5+" and AT_BASE_PLATFORM will be "power6". The idea is
that AT_PLATFORM indicates the instruction set supported, while
AT_BASE_PLATFORM indicates the underlying microarchitecture.
If the architecture has defined ELF_BASE_PLATFORM, copy that value to
the user stack in the same manner as ELF_PLATFORM.
Signed-off-by: Nathan Lynch <ntl@pobox.com>
Acked-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Benjamin Herrenschmidt <benh@kernel.crashing.org>
diff --git a/fs/binfmt_elf.c b/fs/binfmt_elf.c
index 639d2d8..742c8f5 100644
--- a/fs/binfmt_elf.c
+++ b/fs/binfmt_elf.c
@@ -131,6 +131,15 @@
#define STACK_ALLOC(sp, len) ({ sp -= len ; sp; })
#endif
+#ifndef ELF_BASE_PLATFORM
+/*
+ * AT_BASE_PLATFORM indicates the "real" hardware/microarchitecture.
+ * If the arch defines ELF_BASE_PLATFORM (in asm/elf.h), the value
+ * will be copied to the user stack in the same manner as AT_PLATFORM.
+ */
+#define ELF_BASE_PLATFORM NULL
+#endif
+
static int
create_elf_tables(struct linux_binprm *bprm, struct elfhdr *exec,
unsigned long load_addr, unsigned long interp_load_addr)
@@ -142,7 +151,9 @@
elf_addr_t __user *envp;
elf_addr_t __user *sp;
elf_addr_t __user *u_platform;
+ elf_addr_t __user *u_base_platform;
const char *k_platform = ELF_PLATFORM;
+ const char *k_base_platform = ELF_BASE_PLATFORM;
int items;
elf_addr_t *elf_info;
int ei_index = 0;
@@ -172,6 +183,19 @@
return -EFAULT;
}
+ /*
+ * If this architecture has a "base" platform capability
+ * string, copy it to userspace.
+ */
+ u_base_platform = NULL;
+ if (k_base_platform) {
+ size_t len = strlen(k_base_platform) + 1;
+
+ u_base_platform = (elf_addr_t __user *)STACK_ALLOC(p, len);
+ if (__copy_to_user(u_base_platform, k_base_platform, len))
+ return -EFAULT;
+ }
+
/* Create the ELF interpreter info */
elf_info = (elf_addr_t *)current->mm->saved_auxv;
/* update AT_VECTOR_SIZE_BASE if the number of NEW_AUX_ENT() changes */
@@ -209,6 +233,10 @@
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->interp_flags & BINPRM_FLAGS_EXECFD) {
NEW_AUX_ENT(AT_EXECFD, bprm->interp_data);
}