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x86-64, compat: Retruncate rax after ia32 syscall entry tracing

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In commit d4d6715, we reopened an old hole for a 64-bit ptracer touching a
32-bit tracee in system call entry.  A %rax value set via ptrace at the
entry tracing stop gets used whole as a 32-bit syscall number, while we
only check the low 32 bits for validity.

Fix it by truncating %rax back to 32 bits after syscall_trace_enter,
in addition to testing the full 64 bits as has already been added.

Reported-by: Ben Hawkes <hawkes@sota.gen.nz>
Signed-off-by: Roland McGrath <roland@redhat.com>
Signed-off-by: H. Peter Anvin <hpa@linux.intel.com>
This commit is contained in:
Roland McGrath 2010-09-14 12:22:58 -07:00 committed by H. Peter Anvin
parent 36d001c70d
commit eefdca043e
1 changed files with 7 additions and 1 deletions
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8
arch/x86/ia32/ia32entry.S
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@ -50,7 +50,12 @@
/*
* Reload arg registers from stack in case ptrace changed them.
* We don't reload %eax because syscall_trace_enter() returned
* the value it wants us to use in the table lookup.
* the %rax value we should see. Instead, we just truncate that
* value to 32 bits again as we did on entry from user mode.
* If it's a new value set by user_regset during entry tracing,
* this matches the normal truncation of the user-mode value.
* If it's -1 to make us punt the syscall, then (u32)-1 is still
* an appropriately invalid value.
*/
.macro LOAD_ARGS32 offset, _r9=0
.if \_r9
@ -60,6 +65,7 @@
movl \offset+48(%rsp),%edx
movl \offset+56(%rsp),%esi
movl \offset+64(%rsp),%edi
movl %eax,%eax /* zero extension */
.endm
.macro CFI_STARTPROC32 simple