Re: [PATCH v4 1/2] binfmt_flat: allow not offsetting data start
From: Palmer Dabbelt
Date: Fri Apr 23 2021 - 00:05:05 EST
On Thu, 22 Apr 2021 05:00:32 PDT (-0700), Damien Le Moal wrote:
On 2021/04/18 11:38, Greg Ungerer wrote:
On 17/4/21 2:54 pm, Damien Le Moal wrote:
On 2021/04/17 13:52, Greg Ungerer wrote:
On 17/4/21 11:10 am, Damien Le Moal wrote:
Commit 2217b9826246 ("binfmt_flat: revert "binfmt_flat: don't offset
the data start"") restored offsetting the start of the data section by
a number of words defined by MAX_SHARED_LIBS. As a result, since
MAX_SHARED_LIBS is never 0, a gap between the text and data sections
always exists. For architectures which cannot support a such gap
between the text and data sections (e.g. riscv nommu), flat binary
programs cannot be executed.
To allow an architecture to request no data start offset to allow for
contiguous text and data sections for binaries flagged with
FLAT_FLAG_RAM, introduce the new config option
CONFIG_BINFMT_FLAT_NO_DATA_START_OFFSET. Using this new option, the
macro DATA_START_OFFSET_WORDS is conditionally defined in binfmt_flat.c
to MAX_SHARED_LIBS for architectures tolerating or needing the data
start offset (CONFIG_BINFMT_FLAT_NO_DATA_START_OFFSET disabled case)
and to 0 when CONFIG_BINFMT_FLAT_NO_DATA_START_OFFSET is enabled.
DATA_START_OFFSET_WORDS is used in load_flat_file() to calculate the
data section length and start position.
Signed-off-by: Damien Le Moal <damien.lemoal@xxxxxxx>
---
fs/Kconfig.binfmt | 3 +++
fs/binfmt_flat.c | 19 ++++++++++++++-----
2 files changed, 17 insertions(+), 5 deletions(-)
diff --git a/fs/Kconfig.binfmt b/fs/Kconfig.binfmt
index c6f1c8c1934e..06fb7a93a1bd 100644
--- a/fs/Kconfig.binfmt
+++ b/fs/Kconfig.binfmt
@@ -112,6 +112,9 @@ config BINFMT_FLAT_ARGVP_ENVP_ON_STACK
config BINFMT_FLAT_OLD_ALWAYS_RAM
bool
+config BINFMT_FLAT_NO_DATA_START_OFFSET
+ bool
+
config BINFMT_FLAT_OLD
bool "Enable support for very old legacy flat binaries"
depends on BINFMT_FLAT
diff --git a/fs/binfmt_flat.c b/fs/binfmt_flat.c
index b9c658e0548e..1dc68dfba3e0 100644
--- a/fs/binfmt_flat.c
+++ b/fs/binfmt_flat.c
@@ -74,6 +74,12 @@
#define MAX_SHARED_LIBS (1)
#endif
+#ifdef CONFIG_BINFMT_FLAT_NO_DATA_START_OFFSET
+#define DATA_START_OFFSET_WORDS (0)
+#else
+#define DATA_START_OFFSET_WORDS (MAX_SHARED_LIBS)
+#endif
+
struct lib_info {
struct {
unsigned long start_code; /* Start of text segment */
@@ -560,6 +566,7 @@ static int load_flat_file(struct linux_binprm *bprm,
* it all together.
*/
if (!IS_ENABLED(CONFIG_MMU) && !(flags & (FLAT_FLAG_RAM|FLAT_FLAG_GZIP))) {
+
Random white space change...
Don't worry about re-spinning though, I will just edit this chunk out.
Oops. Sorry about that. I should have better checked :)
/*
* this should give us a ROM ptr, but if it doesn't we don't
* really care
@@ -576,7 +583,8 @@ static int load_flat_file(struct linux_binprm *bprm,
goto err;
}
- len = data_len + extra + MAX_SHARED_LIBS * sizeof(unsigned long);
+ len = data_len + extra +
+ DATA_START_OFFSET_WORDS * sizeof(unsigned long);
len = PAGE_ALIGN(len);
realdatastart = vm_mmap(NULL, 0, len,
PROT_READ|PROT_WRITE|PROT_EXEC, MAP_PRIVATE, 0);
@@ -591,7 +599,7 @@ static int load_flat_file(struct linux_binprm *bprm,
goto err;
}
datapos = ALIGN(realdatastart +
- MAX_SHARED_LIBS * sizeof(unsigned long),
+ DATA_START_OFFSET_WORDS * sizeof(unsigned long),
FLAT_DATA_ALIGN);
pr_debug("Allocated data+bss+stack (%u bytes): %lx\n",
@@ -622,7 +630,8 @@ static int load_flat_file(struct linux_binprm *bprm,
memp_size = len;
} else {
- len = text_len + data_len + extra + MAX_SHARED_LIBS * sizeof(u32);
+ len = text_len + data_len + extra +
+ DATA_START_OFFSET_WORDS * sizeof(u32);
len = PAGE_ALIGN(len);
textpos = vm_mmap(NULL, 0, len,
PROT_READ | PROT_EXEC | PROT_WRITE, MAP_PRIVATE, 0);
@@ -638,7 +647,7 @@ static int load_flat_file(struct linux_binprm *bprm,
realdatastart = textpos + ntohl(hdr->data_start);
datapos = ALIGN(realdatastart +
- MAX_SHARED_LIBS * sizeof(u32),
+ DATA_START_OFFSET_WORDS * sizeof(u32),
FLAT_DATA_ALIGN);
reloc = (__be32 __user *)
@@ -714,7 +723,7 @@ static int load_flat_file(struct linux_binprm *bprm,
ret = result;
pr_err("Unable to read code+data+bss, errno %d\n", ret);
vm_munmap(textpos, text_len + data_len + extra +
- MAX_SHARED_LIBS * sizeof(u32));
+ DATA_START_OFFSET_WORDS * sizeof(u32));
goto err;
}
}
Thanks, otherwise looks good.
Acked-by: Greg Ungerer <gerg@xxxxxxxxxxxxxx>
I will push this into my m68knommu tree, for-next branch.
I just carry the flat format changes in that tree now to make my life easier.
Great. Thanks !
Are you taking both patches or should Plamer take the riscv Kconfig change
through his tree ?
I am happy to take both.
Palmer?
Palmer,
Ping !
I already Ack'd it, in the thread where we couldn't find the maintainer.
Keeping these togther is fine with me, and it seems easiest.
--
Damien Le Moal
Western Digital Research