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authorH. Peter Anvin <hpa@zytor.com>2009-04-14 21:52:50 -0700
committerH. Peter Anvin <hpa@zytor.com>2009-04-14 21:52:50 -0700
commit51c8b419b201678ea27edfa9d037c851f18b7fb5 (patch)
tree566b8d74bcffd41fb392df83e8db28d77b4977f7 /gpxe/src/arch/i386
parent927a28f0f852b31950fd9d4f9d96049397d1eaa1 (diff)
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gpxe: Don't use "lret $2" to return from an interrupt
Using "lret $2" to return from an interrupt causes interrupts to be disabled in the calling program, since the INT instruction will have disabled interrupts. Instead, patch CF on the stack and use iret to return. Interestingly, the original PC BIOS had this bug in at least one place. Signed-off-by: H. Peter Anvin <hpa@zytor.com>
Diffstat (limited to 'gpxe/src/arch/i386')
-rw-r--r--gpxe/src/arch/i386/firmware/pcbios/e820mangler.S27
-rw-r--r--gpxe/src/arch/i386/firmware/pcbios/fakee820.c5
-rw-r--r--gpxe/src/arch/i386/interface/pxe/pxe_entry.S7
3 files changed, 26 insertions, 13 deletions
diff --git a/gpxe/src/arch/i386/firmware/pcbios/e820mangler.S b/gpxe/src/arch/i386/firmware/pcbios/e820mangler.S
index 4ba3fb14..decb0835 100644
--- a/gpxe/src/arch/i386/firmware/pcbios/e820mangler.S
+++ b/gpxe/src/arch/i386/firmware/pcbios/e820mangler.S
@@ -490,6 +490,18 @@ get_mangled_e820:
.size get_mangled_e820, . - get_mangled_e820
/****************************************************************************
+ * Set/clear CF on the stack as appropriate, assumes stack is as it should
+ * be immediately before IRET
+ ****************************************************************************
+ */
+patch_cf:
+ pushw %bp
+ movw %sp, %bp
+ setc 8(%bp) /* Set/reset CF; clears PF, AF, ZF, SF */
+ popw %bp
+ ret
+
+/****************************************************************************
* INT 15,e820 handler
****************************************************************************
*/
@@ -500,7 +512,8 @@ int15_e820:
popw %ds
call get_mangled_e820
popw %ds
- lret $2
+ call patch_cf
+ iret
.size int15_e820, . - int15_e820
/****************************************************************************
@@ -512,7 +525,7 @@ int15_e801:
/* Call previous handler */
pushfw
lcall *%cs:int15_vector
- pushfw
+ call patch_cf
/* Edit result */
pushw %ds
pushw %cs:rm_ds
@@ -524,9 +537,7 @@ int15_e801:
xchgw %ax, %cx
xchgw %bx, %dx
popw %ds
- /* Restore flags returned by previous handler and return */
- popfw
- lret $2
+ iret
.size int15_e801, . - int15_e801
/****************************************************************************
@@ -538,16 +549,14 @@ int15_88:
/* Call previous handler */
pushfw
lcall *%cs:int15_vector
- pushfw
+ call patch_cf
/* Edit result */
pushw %ds
pushw %cs:rm_ds
popw %ds
call patch_1m
popw %ds
- /* Restore flags returned by previous handler and return */
- popfw
- lret $2
+ iret
.size int15_88, . - int15_88
/****************************************************************************
diff --git a/gpxe/src/arch/i386/firmware/pcbios/fakee820.c b/gpxe/src/arch/i386/firmware/pcbios/fakee820.c
index e171edfd..552bf41d 100644
--- a/gpxe/src/arch/i386/firmware/pcbios/fakee820.c
+++ b/gpxe/src/arch/i386/firmware/pcbios/fakee820.c
@@ -63,6 +63,8 @@ void fake_e820 ( void ) {
"cmpl $0x534d4150, %%edx\n\t"
"jne 99f\n\t"
"pushaw\n\t"
+ "movw %%sp, %%bp\n\t"
+ "andb $~0x01, 22(%%bp)\n\t" /* Clear return CF */
"leaw e820map(%%bx), %%si\n\t"
"cs rep movsb\n\t"
"popaw\n\t"
@@ -73,8 +75,7 @@ void fake_e820 ( void ) {
"xorl %%ebx,%%ebx\n\t"
"\n1:\n\t"
"popfw\n\t"
- "clc\n\t"
- "lret $2\n\t"
+ "iret\n\t"
"\n99:\n\t"
"popfw\n\t"
"ljmp *%%cs:real_int15_vector\n\t" )
diff --git a/gpxe/src/arch/i386/interface/pxe/pxe_entry.S b/gpxe/src/arch/i386/interface/pxe/pxe_entry.S
index 22ef4181..0e8c8e2d 100644
--- a/gpxe/src/arch/i386/interface/pxe/pxe_entry.S
+++ b/gpxe/src/arch/i386/interface/pxe/pxe_entry.S
@@ -199,9 +199,12 @@ pxe_int_1a:
shll $4, %edx
addl $pxenv, %edx
movw $0x564e, %ax
+ pushw %bp
+ movw %sp, %bp
+ andb $~0x01, 8(%bp) /* Clear CF on return */
+ popw %bp
popfw
- clc
- lret $2
+ iret
1: /* INT 1A,other - pass through */
popfw
ljmp *%cs:pxe_int_1a_vector