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arm: Remove wrong ldr from _dl_start_user (BZ 31339)

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The commit 49d877a80b (arm: Remove
_dl_skip_args usage) removed the _SKIP_ARGS literal, which was
previously loader to r4 on loader _start.  However, the cleanup did not
remove the following 'ldr r4, [sl, r4]' on _dl_start_user, used to check
to skip the arguments after ld self-relocations.

In my testing, the kernel initially set r4 to 0, which makes the
ldr instruction just read the _GLOBAL_OFFSET_TABLE_.  However, since r4
is a callee-saved register; a different runtime might not zero
initialize it and thus trigger an invalid memory access.

Checked on arm-linux-gnu.

Reported-by: Adrian Ratiu <adrian.ratiu@collabora.com>
Reviewed-by: Szabolcs Nagy <szabolcs.nagy@arm.com>
(cherry picked from commit 1e25112dc0)
This commit is contained in:
Adhemerval Zanella 2024-02-05 16:10:24 +00:00
parent 6d1e3fb07b
commit 63295e4fda
1 changed files with 0 additions and 1 deletions
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1
sysdeps/arm/dl-machine.h
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@ -139,7 +139,6 @@ _start:\n\
_dl_start_user:\n\ _dl_start_user:\n\
adr r6, .L_GET_GOT\n\ adr r6, .L_GET_GOT\n\
add sl, sl, r6\n\ add sl, sl, r6\n\
ldr r4, [sl, r4]\n\
@ save the entry point in another register\n\ @ save the entry point in another register\n\
mov r6, r0\n\ mov r6, r0\n\
@ get the original arg count\n\ @ get the original arg count\n\